Here is another thread on the topic: http://modthesims.info/t/546736 -- I figure it comes down to the OS in the end, and as far as I can see nobody has supplied that info, so YMMV.
By the way the only package I've seen so far that can cause issues when merging is the "novelist" package that's distributed with the
Maxis CC guide -- this cannot be re-saved with s4pe, because it has a different compression format from everything else, but C+Ping the content into a new package works fine (so merging would only work one way: one can merge its content into another package, but not merge other stuff into that package) -- apart from that, I know of no actual evidence to those claims. Allegedly there are some other, very early CC packages that are using that type of compression (?), I don't know what they are, but if that's the case it comes down to the individual packages and is not a general issue.
