As this issue seems to have been resolved with new drivers I'll mark this thread as solved now.
AMD has released the 14.1 drivers for Mantle support. Although it needs a 7xxx or above card to use Mantle, I'm wondering if there might be some other fixes that help the memory leak issue. There's no specific mention of it in the release notes though
http://support.amd.com/en-us/kb-articles/Pages/latest-catalyst-windows-beta.aspx
I'll play some time tonight to see if it helps.
I've tried a number of things to get rid of this issue, but got it solved only by running BF4 in x86 mode (can be changed in Origin).
When I played on Win 7 before it also never happened, only on Win 8 (8.1)
Just played with the new drivers. It seems either the new 14.1 drivers or the latest update have just made it worse. Before I would get 2 or 3 map changes before it would happen, now it happens after the first map change.
Only way I've found to prevent it is still alt-tab at end of round, but that's a real pain if you forget.
