The test case (to follow) has a PRE element with "overflow: auto" inside a TABLE with "width: 100%". Clicking on the down arrow on the scroll bar causes the element box to "grow", as evident by the scroll bar jumping to the right. Since the scroll bar shouldn't be there (bug 55586), this bug might be INVALID.
Dividing up claytons bugs to triage
appears to be a layout issue
Let me add a comment to the latest uploaded testcase. It seems overflow: auto causes this "scrollbar funkiness" when used on an element within a table. It appears to be a general problem. Problem encountered in Mozilla 0.6, NS6, various other Mozilla builds on both WIN32 and Mac platforms.
Moving to m1.0.1 and reassigning to attinasi.
overflow:auto is no longer causing growth. marking WORKSFORME.