I've got a strange error with IE8 and postcode lookups. It may not be postcode lookups as such that's causing it - just an AJAX call that modifies a select. I've set up a test page here. If you click on Find Address, and then double click (quite quickly) on one of the addresses that is within the boundary of the red-bordered div, you see the below bug in IE8.
Note: I'm finding it inconsistent to reproduce the bug, but if you scroll the list of addresses right to the bottom and then double click fast on Holly Cottage it should reproduce the bug.
If anyone can shed on light on this quirky behaviour it'd be much appreciated. Is this an IE8 bug?