I was finding I was having a very frustrating issue when using Adobe Premiere Pro to do video editing, where it would automatically zoom out of a sequence/timeline when I went and moved a clip somewhere (even if just moving it slightly to the left to line up with another clip).
First of all, let me describe my set up when doing video editing. I use a Mac Pro (Late 2013) with a Wacom Cintiq 22HD graphics tablet, and run Adobe After Effects CC 2017. I also use the onscreen keyboard you get on Macs and have 'sticky keys' set to 'on' in accessibility so that the function keys, like shift and command, will hold until I press the next key (essential for shortcuts etc when using the onscreen keyboard)...though it appears that the use of sticky keys doesn't seem to be the cause of the issue as I can get the same issue when sticky keys is set to 'off'.
I googled the problem to find a lot of other people having the same issue, but no solution. Well, there were a few solutions suggested but none of them sorted it. The only 'solution' was to restart Premiere Pro, which worked but was frustrating to say the least.
When using the onscreen keyboard I have always noticed that sometimes random keys on the keyboard are shaded darker, which usually happens to tell you that this key is being held down; so while typing i'd see the 'a' key, the 's' key and the 'w' key all shaded dark (for example) but never caused and apparent issue (nothing happened like lots of aaaaa's being produced or anything) so assumed it was a weird glitch.
However, when i was doing my video editing and found this zooming out issue started, I noticed that the minus key (-) was always shaded darker. Every time. The next time the issue occurred, I pressed the '-' key and that took away the dark shading...afterwards the zooming out issue stopped! It's no coincidence that the minus key is used alongside the plus key to zoom out and in, so obviously the key was indeed being depressed in some way and causing the timeline to zoom out.
Hopefully this will help many of you with the same problem, or if you don't use the onscreen keyboard then maybe there's a chance it's still something to do with the minus key.
Get in touch if you find any other solutions or have similar issues.