Comment 5 for bug 1504560

No, not every time. My system is fast I think, a Lenovo ThinkPad T450s that I set up just last week. I have a lot of applications open right now so it's a little bogged down, and now the double click is working about a third of the time. I tried slow and quick double clicks, but I'm not seeing any correlation. I tried disabling window geometry hints, and the behavior did not change.

Oh, but I did just find a correlation. For the purpose of this description, I'm going to say a double click is pressing down; releasing ("up"); has short, medium, and long waits; and I can pause at any time. Now, a normal double click for me is "down-medium-up-long-down-medium-up". But, if I change my action to "down-medium-up-long-down-pause", and then move my mouse, I see that the separator flashed, came back to my mouse, and is now moving with my mouse. But, if I do "down-medium-up-long-down-short-up", (and it is pretty difficult to get that short wait short enough), the splitter gets rebalanced successfully.

I think you've hit the nail on the head there with your suspicion, from my experience.