2017.05: Undo is not undoing sometimes

I just started noticing this in 2017.05 update.

Occasionally I will hit CTRL-Z to undo some clip edits, but then it does *not* return to its previous state. It seems to occur mostly with clip stretching.

It's happening enough that I know it's not me or "user error". But not so much that it's unusable. My guess is that undo is failing every 50 clip edits. So if I'm doing a lot of edits in a session then I'll notice it a few times. Luckily I frequently save so I can do a "hard undo".

The problem manifests itself with the edited clip returning in a different state or position. Or the contents of the stretched clip are not in the same position as before.

I've seen this in several projects too, new and old.