Yeah, there is a new problem on Macs with the threshold bar.
Bob put in a fix into the *latest* build of AFNI (June 3, I believe)-- so you can get that one. The jittering will be gone.
What *will* happen sometimes is that the threshold bar will shrink to about 50% size or so; the "Thr" at the top of the threshold bar has now been turned into a button-- left clicking on it will put the threshold slider bar back to its full size (rightclicking on it still has its usual menu of options).
This has been a weird annoyance via motif on Macs; we are teaching a Bootcamp this week, so the ability to focus on this new "feature" has been short, hence the quick fix. There might be another fix rolling out later/in the nearish future, but teaching+OHBM duties will probably cause some delay in this.
--pt
