PR #3531 added this code to throttle scrollbar updates to reduce CPU usage:

But the code skips the last scroll update. If we have 4 updates very quickly, then:

• 1st will set the _lastScrollTime and update the scrollbar
• 2nd will return because the time difference is too small but will reset _lastScrollTime for the next one (BTW why reset? we could skip the next one too)
• 3rd will set the _lastScrollTime and update the scrollbar
• 4th will return because the time difference is too small but will reset _lastScrollTime for the next one

So we missed the last update (the 4th) and now the scrollbar has invalid value.

@skyline75489