I was experiencing the same issue described in the debian bug #374604: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=374604 As described there, this is resolveable by bumping the version of evolution-exchange to 2.6.3-r3. I did so with an ebuild that applies the pertinent patch from debian (available at http://packages.debian.org/unstable/gnome/evolution-exchange) I will attach the rough ebuild and patch to this bug report. I assume a more elegant version bump is also possible, but this was a quick and dirty check to see if the problem went away. Applying the patch from debian resolved the issue.
Created attachment 94238 [details] evolution-exchange/evolution-exchange-2.6.2-r3.ebuild
Created attachment 94239 [details, diff] Patch to bump evolution-exchange to 2.6.2-r3
Created attachment 94240 [details, diff] Patch to bump evolution-exchange to 2.6.2-r3
Is this still a problem in the 2.8 or 2.10 series as in portage?
Seems that this patch was incorporated before 2.8. Thus this bug is fixed in the currently stable evolution. Reopen, please, if I'm wrong.