When a text field has focus, but the text is not selected, and the web view is scrolled, the old content at the top or bottom (where the new content will appear) draws in two places (the old and new location) before the new content replaces the old. The new content should just pop in without the old content drawing twice for that split second. I'm guessing this is just our inefficient redraw bug (bug 280982), but I'm filing just to make sure.
Looks like this is actually related to 54153; marking dependant.
This is almost certainly because we were flushing the port buffer for the caret. Bug 301774 may have helped here. Can someone test?
Please retest in current trunk builds? There might be a difference now that bug 287813 is fixed.
I'm not seeing this in current builds. If anyone still sees it (and ideally, has a good testcase), please re-open.
Verifying that I no longer see this.