Xorg lock with kmail

I've been experiencing xorg locks lately (only the mouse cursor moves) and 
found out that if I kill kmail from another console xorg is happy again and 
switching back to it and moving the mouse is sufficient to have a fully 
functional desktop.

Gentoo here, the package versions are:
kde 1.13.6 (kdepim 4.6 gentoo devs stopped updating kdepim until they think 
it's stable enough)
kmail 4.4.10
xorg-x11 7.4
xorg-server 1.9.4
nvidia-drivers 260.19.36

Does someone have an insight on this?
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