Unexpected Client Mashup

Tonight Makal and I were out at a shop, and on the way out I picked up this local weekly newspaper. I'd done an ad for a new client that was in last week's edition, and forgot to pick it up. Today the new edition came out, which I forgot when realizing I still hadn't seen the ad and grabbed a copy. So I'm flipping through the pages, reading all the amusing "alternatives" personal ads and such, looking for the ad that really wasn't there. Except (except!) suddenly I come across an ad I did recognize. Because it was an ad I did for another client several months ago. At first I thought that somehow I submitted the wrong ad, but the correct copy was there. Not only was it the write words, but it was the same phrasing and alignment of the text I did for last week's paper. With the artwork for the older client. ?!?! Now, I know these two women are friends, but how is it that one got the image from the other's ad (for an entirely different publication)? And, if I didn't design this particular ad, who did they pay to splice together the two different advertisements that I originally designed? Ack. Maybe there's a reader out there with some advice for me. Makal and I were discussing it being my intellectual property, since I designed them, and yet on the other hand it was work they paid me for (though technically, I haven't yet been paid for the the ad in last week's paper...) which makes it there property. I guess. I dunno? See, this is why I have no idea how to treat it. Never had this happen before, where I have enough clients for work to start overlapping; or for me to have enough happy clients who think the two ads were good enough to combine into a third, even greater ad. Aha, maybe that's the way I should be looking at it—some variation of the "imitation" cliché. Eh, but still. It just felt so shocking to come across unexpectedly, especially since she (the newer client) communicated with me so readily on the first ad for last week. And I just got done doing a new ad for the older client. Meh, I think right now I'm just caught up in the moment and feeling confused about it. I'll have to figure something out soon at least, since I need to be talking with both sometime this weekend. Oh the woes of attempting self-employment. :P