I have the same behavior on Vista x64, with dual ATIs HD3870s / Catalyst 10.6
I *believe* this is caused by a change in the DirectX functions for x64, as I hadn't noticed this issue until relatively recently (maybe a month or 2 ago).
It'd be good if anybody that's using Vista x32 or Win7 x32 could confirm if it happens on that version, as I don't have it available atm.
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As far as an immediate solution, I'm afraid there isn't, -or I haven't found one- but we'll add it to the list of things to review and see if we can find an answer for a next release.