Use Visual Editor in a small browser window (maybe 30 lines tall, and narrow enough so that the editor tool bar at the top takes up two rows) to edit a page on Wikipedia, highlight a common word, and hit Ctrl-K (to create a link). The link-target-chooser window pops up, and if it is tall enough (i.e. contains enough entries), then the highlighted word will scroll out of view. It remains out of view even after choosing the link target or canceling the target-chooser window.
This also happen for other pop-up windows, like the link window that appears when clicking on a link, but those windows are smaller and therefore the effect is rarer.