The onMouseOver and onMouseOut events are triggered at every mouse movement over the test in a DIV, as in the following, <DIV STYLE="width: 300px; height: 30px; border: 1px solid black;" onMouseOver="alert('Irritaing, huh?');">This is a DIV</DIV>
Created attachment 4774 [details] testcase
of onMouseOver should only trigger once, when you enter the element, this IS a bug. and yes, it is annoying.
It seems to be related to the text content. Nice testcase.
This happens to me too. It doesn't affect Divs, but text elements. It goes fine with divs and images, but it gives problem with elements containing text.
I can reproduce with WebKit-417.9 but not with TOT (r13060). Is the bug completely fixed in TOT or is there a test case where it still shows (perhaps along the lines of comment #4)?
A test for this has been landed with a fix for bug 3439. Please open a new bug (or bugs) if there are other examples of this behavior, still reproducible with current nightly builds.