Since the update the scrollwheel seems to "work" erratically when zooming a viewer, reacting too late and then zooming too fast. Scrolling works as it should with the other panels.
I'm on a Mac 10.8.5.
We have verified this bug internally in After Effects 12.1 on Mac OS, with a variety of mouse hardware. The problem does not occur on Windows.
The issue is related to scrolling speed. If you scroll very slowly, the scroll action is not recognized. If you scroll at a faster speed, the scrolling action is recognized. This is true for scrolling in all panels, not just viewers; it's possible you only see it in viewers because your intent to zoom via scroll requires more precision.
Apologies for the bug. We are investigating the cause and a fix. In the meantime, my recommendation is that when you need to zoom in via small increments in a viewer, use the keyboard shortcuts, or switch briefly to the Zoom tool.
When can we expect a fix? This is a huge slow down and causes a lot of frustration.
I don't want to give you an expectation of a date for a fix, because as of today we have neither fixed the issue internally nor announced the details of our next release.
What I will tell you is that this bug is being worked on by one of our developers, that it is scheduled to be fixed for our next release, and that release is probably going to be out sooner than you expect.
Again, apologies for the bug and the frustrations.
Not to muddy up the topic, but the scroll wheel issue seams to be also manifesting in Premiere CC, when using the scroll wheel as a shuttle in the Program Monitor. If I spin the wheel unusually fast, I can get a few frames to advance or rewind. Any normal scrubbing is not possible.