Another example attached:
The underlay is the "fit" dataset - shown in black.
For Dataset#N I have chosen: "fit" dataset in dk-blue and "time course" data set in limegreen.

So the Dataset#N "fit" dataset is clearly different than the "underlay" "fit" data set.

Also, point 1- above is not valid - it seems that the orientation of the data sets is what is wrong. The plot window seems to be getting data from the wrong voxel - I'm not sure where.

I've done 3dinfo on both fit and time course, and nothing seems out of the ordinary:

%> 3dinfo rc_t177sss5.r1tc.tkTfit+orig

Dataset File: rc_t177sss5.r1tc.tkTfit+orig
Identifier Code: "pv,<?ZmzDhBUcB&*mIz`qD[` Creation Date: Mon Jan 21 01:26:28 2008
Dataset Type: Other MRI (-omri)
Byte Order: LSB_FIRST [this CPU native = MSB_FIRST]
Storage Mode: BRIK file
Data Axes Orientation:
first (x) = Inferior-to-Superior
second (y) = Left-to-Right
third (z) = Posterior-to-Anterior [-orient ILP]
R-to-L extent: -14.883 [R] -to- 14.883 [L] -step- 0.234 mm [128 voxels]
A-to-P extent: -2.250 [A] -to- 2.250 [P] -step- 1.500 mm [ 4 voxels]
I-to-S extent: -14.883 -to- 14.883 [S] -step- 0.234 mm [128 voxels]
Number of time steps = 36 Number of values at each pixel = 1
Time step = 1.000s Origin = 0.000s
-- At sub-brick #0 '#0' datum type is float: 0 to 2.67619
-- At sub-brick #1 '#1' datum type is float: 0 to 2.67619
-- At sub-brick #2 '#2' datum type is float: 0 to 2.67619
-- At sub-brick #3 '#3' datum type is float: 0 to 2.67619
-- At sub-brick #4 '#4' datum type is float: 0 to 2.67619
-- At sub-brick #5 '#5' datum type is float: 0 to 2.67619
-- At sub-brick #6 '#6' datum type is float: 0 to 2.67619
-- At sub-brick #7 '#7' datum type is float: 0 to 2.67619
-- At sub-brick #8 '#8' datum type is float: 0 to 2.67619
-- At sub-brick #9 '#9' datum type is float: 0 to 22.7928
-- At sub-brick #10 '#10' datum type is float: 0 to 18.0331
-- At sub-brick #11 '#11' datum type is float: 0 to 19.3882
-- At sub-brick #12 '#12' datum type is float: 0 to 19.986
-- At sub-brick #13 '#13' datum type is float: 0 to 20.3088
-- At sub-brick #14 '#14' datum type is float: 0 to 19.8474
-- At sub-brick #15 '#15' datum type is float: 0 to 19.2144
-- At sub-brick #16 '#16' datum type is float: 0 to 18.4083
-- At sub-brick #17 '#17' datum type is float: 0 to 17.6779
-- At sub-brick #18 '#18' datum type is float: 0 to 16.821
-- At sub-brick #19 '#19' datum type is float: 0 to 16.2672
-- At sub-brick #20 '#20' datum type is float: 0 to 15.8313
-- At sub-brick #21 '#21' datum type is float: 0 to 15.1673
-- At sub-brick #22 '#22' datum type is float: 0 to 14.8615
-- At sub-brick #23 '#23' datum type is float: 0 to 14.4847
-- At sub-brick #24 '#24' datum type is float: 0 to 14.2221
-- At sub-brick #25 '#25' datum type is float: 0 to 13.9048
-- At sub-brick #26 '#26' datum type is float: 0 to 13.3025
-- At sub-brick #27 '#27' datum type is float: 0 to 12.8544
-- At sub-brick #28 '#28' datum type is float: 0 to 12.555
-- At sub-brick #29 '#29' datum type is float: 0 to 12.2746
-- At sub-brick #30 '#30' datum type is float: 0 to 12.7771
-- At sub-brick #31 '#31' datum type is float: 0 to 12.1564
-- At sub-brick #32 '#32' datum type is float: 0 to 11.9308
-- At sub-brick #33 '#33' datum type is float: 0 to 11.8503
-- At sub-brick #34 '#34' datum type is float: 0 to 14.4537
-- At sub-brick #35 '#35' datum type is float: 0 to 14.6399

----- HISTORY -----
[Mon Jan 21 01:26:28 2008] created by IDL7.0 Win32 write_afni_brick

%> cat rc_t177sss5.r1tc.tkTfit+orig.HEAD

type = string-attribute
name = HISTORY_NOTE
count = 68
'[Mon Jan 21 01:26:28 2008] created by IDL7.0 Win32 write_afni_brick~

type = string-attribute
name = TYPESTRING
count = 15
'3DIM_HEAD_ANAT~

type = string-attribute
name = IDCODE_STRING
count = 27
'"pv,<?ZmzDhBUcB&*mIz`qD[`~

type = string-attribute
name = IDCODE_DATE
count = 25
'Mon Jan 21 01:26:28 2008~

type = integer-attribute
name = SCENE_DATA
count = 8
0 10 0 -999 -999
-999 -999 -999

type = string-attribute
name = LABEL_1
count = 29
'rc_t177sss5.r1tc.tkTfit+orig~

type = string-attribute
name = LABEL_2
count = 7
'Prost!~

type = string-attribute
name = DATASET_NAME
count = 31
'./rc_t177sss5.r1tc.tkTfit+orig~

type = integer-attribute
name = ORIENT_SPECIFIC
count = 3
4 1 2

type = float-attribute
name = ORIGIN
count = 3
-14.88281 14.88281 2.250000

type = float-attribute
name = DELTA
count = 3
0.2343750 -0.2343750 -1.500000

type = float-attribute
name = BRICK_STATS
count = 72
0.0000000 2.676194 0.0000000 2.676194 0.0000000
2.676194 0.0000000 2.676194 0.0000000 2.676194
0.0000000 2.676194 0.0000000 2.676194 0.0000000
2.676194 0.0000000 2.676194 0.0000000 22.79276
0.0000000 18.03315 0.0000000 19.38823 0.0000000
19.98603 0.0000000 20.30877 0.0000000 19.84738
0.0000000 19.21443 0.0000000 18.40829 0.0000000
17.67789 0.0000000 16.82101 0.0000000 16.26716
0.0000000 15.83131 0.0000000 15.16731 0.0000000
14.86150 0.0000000 14.48471 0.0000000 14.22215
0.0000000 13.90481 0.0000000 13.30248 0.0000000
12.85441 0.0000000 12.55503 0.0000000 12.27465
0.0000000 12.77710 0.0000000 12.15638 0.0000000
11.93081 0.0000000 11.85029 0.0000000 14.45370
0.0000000 14.63987

type = integer-attribute
name = TAXIS_NUMS
count = 8
36 0 77002 -999 -999
-999 -999 -999

type = float-attribute
name = TAXIS_FLOATS
count = 8
0 1 0 0 0
-999999 -999999 -999999

type = integer-attribute
name = DATASET_RANK
count = 8
3 36 0 0 0
0 0 0

type = integer-attribute
name = DATASET_DIMENSIONS
count = 5
128 128 4 0 0

type = integer-attribute
name = BRICK_TYPES
count = 36
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3

type = float-attribute
name = BRICK_FLOAT_FACS
count = 36
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0

type = string-attribute
name = BYTEORDER_STRING
count = 10
'LSB_FIRST~

type = string-attribute
name = BRICK_LABS
count = 134
'#0~#1~#2~#3~#4~#5~#6~#7~#8~#9~#10~#11~#12~#13~#14~#15~#16~#17~#18~#19~#20~#21~#22~#23~#24~#25~#26~#27~#28~#29~#30~#31~#32~#33~#34~#35~

type = string-attribute
name = BRICK_KEYWORDS
count = 36
'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~