Exceeding scrollback limit breaks GtkScrolledWindow scrolling with enable-fallback-scrolling disabled
Another weird scrolling bug has been found in roxterm which triggers when vte's scrollback limit is set to a small value (in this case, 1000 lines) and the limit is exceeded. After this, I can only scroll up with a touchpad, and there seems to be some sort of overshoot, because I have to scroll a bit more "vigorously"/for longer to get the scrolling started. The mouse wheel doesn't work at all in the "stuck" state, and using the keyboard shortcut for page up only makes the terminal flicker; it looks like it's trying to scroll up but then immediately reverting back to the original position. Unlike the original reporter, resetting the terminal doesn't fix it for me.
Once unstuck with the touchpad, scrolling seems normal with all devices, but there's still something wrong at the limits. Scrolling back to the bottom makes it get stuck again, and scrolling all the way to the top causes the scrollbar to jump all the way to the bottom and get stuck again.
I've also tested without setting enable-fallback-scrolling to false, and in that case the bug doesn't trigger.
I guess this should be linked to #336. I thought it could also be another symptom of gtk#3752, but I can't test that unless gtk!3300 (merged) gets backported to gtk3.
I'm using vte 0.64.1 in Arch Linux; I'm not sure what version the reporter is using.