If I understand correctly (someone please correct me if not) any address you have used before copying the wallet will be perfectly accessible from either copy. As will any coins sent to those addresses, regardless of whether they were sent before or after the split. Speaking as a fairly new user myself, this I think is all most new users would expect, and that part is fine. What is not immediately apparent is that the wallet contains an additional 100 addresses pregenerated for later use. This means when you "add" a new address, it actually takes it from the pregenerated pool. The first 100 address* you add to one wallet will already exist in the copy. Handy, but not perfect. After you go through the 100 address*, then it has to start creating new ones, which won't be in the copy. That's still not terrible, but if you burn through 100 address* on both the original and the copy, then neither wallet will contain a complete set of addresses, that means some Bitcoins will only be available in one or the other (and some will be in both), which does sound like a rather confusing situation.
*I understand some are used up for behind-the-scenes purposes, so you shouldn't expect a full 100 to use directly yourself.

So (again, assuming I've understood all this right myself) it looks like all you would need to avoid these problems is to make one copy your "Primary" wallet, and regularly replace the others with fresh copies of it.

But there's another problem it won't fix. That pregenerated address pool can be helpful, but it can also get you in trouble. Because when you add a "new" address in one copy of the wallet it might already be one you used in a different copy. That could be confusing, e.g. if you unknowingly give the same address to but both Alice and Bob to accept a 5 BTC payment from each, and 5 BTC appears, you might at first thing they both paid, but then you realize it's the same address and you've only been paid once... but by whom?