IS ROMNEY PICKING UP BACHMANN'S VOTES? AND IF SO, WHY?

I usually ignore Rasmussen polls, but I'm wondering if there's value in looking at the new Rasmussen poll of the GOP primary field and the one released in mid-August -- after all, Rasmussen's results seem extremely skewed but not invented outright, so they may reveal real trends even if they're inaccurate. (What I mean is, I think Rasmussen polls honestly but oversamples right-wingers, and that would seem to matter less in an all-GOP poll.)

The Rasmussen numbers for the three most-discussed GOP candidates are as follows:

Perry: 29% in August, 28% now
Romney: 18% in August, 24% now
Bachmann: 13% in August, 8% now

So:

Perry down by 1
Romney up by 6
Bachmann down by 5

That's curious, because here are the extremely similar changes in Gallup polls conducted in August and this month:

Perry up by 2
Romney up by 7
Bachmann down by 5

Hunh? Is Bachmann losing voters to Romney? The Mormon not-quite-hardliner is getting the evangelical hardliner's voters? Former supporters of Ms. Purism Before Electability are abandoning her for Mr. If You Don't Like These Principles I Have Others? Is this really possible? (While Perry, whose numbers seem stable, isn't picking up voters from his hardline soul mate?)

Why would it happen? Is it a consequence of Perry's gender gap -- women don't take to him, so women who are abandoning Bachmann are latching on to Romney? Do Bachmann and Romney share a non-Southern affect that appeals to similar blocs of voters? Do voters really not care about issue positions? Is all this a coincidence?

I'm stumped.