emerge -uDvat world

These are the packages that would be merged, in reverse order:

Calculating world dependencies... done!
[ebuild NS  ] app-crypt/qca-1.0-r2 0 kB
[blocks B   ] <app-crypt/qca-1.0-r3 (is blocking app-crypt/qca-2.0.0-r2)

Total: 1 package (1 in new slot, 1 block), Size of downloads: 0 kB

!!! Error: The above package list contains packages which cannot be installed
!!!     at the same time on the same system.


Can anyone tell me what's causing this? qca version 2 is installed. I can
unmerge and then re-emerge it. Why is the system trying to install version
1? If it's a dependency, shouldn't the depending file be listed?

Thanks in advance.

--
gentoo-user@(protected)