css bug in system.css?

Hi,

I have observed that if a textfield with an autocomplete property is inside a fieldset, and the autocomplete list "overlaps" with a textarea (class="form-textarea resizable required processed"), the items overlapping the textarea are shown, but appear to be behind the textarea content area. (using Firefox v. 2.0.0.12 on windows XP)

I have replicated this behaviour with both, a custom theme, as well as the "garland" and "marvin" theme (I haven't tried any other themes, but I think it applies to all default ones).

I have tracked down a possible cause for this in system.css, line 333

/* Avoid jumping around due to margins collapsing into collapsible fieldset border */
html.js fieldset.collapsible .fieldset-wrapper {
  overflow: auto;
}

If you remove the overflow: auto; property, the autocomplete dropdown works fine (both in Firefox - above mentioned version - and IE7).

Does anyone have any suggestions about the root cause of this buggy behaviour, and any suggestions for a possible workaround other than removing this property?

Thanks,

Kiran