I would like to say it was just a shedding issue, but it's odd that it's both of them. It's also gonna be harder with out pics to try and determine what they could be. Where are they located, what sort of heat source are you using?

You said it happened at their last shed cycle, so they have had them for a few weeks? Are they getting worse? Better? Stayed the same?

Have you separated them from the rest of your collection? Just as a precaution you may want to until you know what you are dealing with being that it's both of them.

I have a snake who shed once and had a white patch of scales appear about the size of a dime. It lasted for a few months until he shed a few more times and it disappeared, being replaced by black (even though the original place was brown and black). In my guy's case his scales were perfect, just missing color. I've heard that this can happen if the old skin separates from the new skin before pigment develops but I have no clue if that's the true case or not. Not sure if this helps but figured I'd share :) Here is a picture of his.

and now:

wow that is wierd! Thanks for sharing the pics!

Sounds like they scraped themselves against something in the cage and pulled off skin that wasn't quite ready to shed (which is what the pictures look like from abi).  since they both did it while in the same cage sounds like there's something in that cage that's a little rough on their skin.  naturally, it's what they're preferring to rub against!

can you take pictures?  those will tell us more!

I have a boa I thought was turning calico. I came to find out he had rubbed himself after escaping from a plastic drawer system I had made (which I have since stopped using lol). Even after a couple sheds he still has some pigment missing on his head but most of the rest seems to have come back.

However, Abi's case is really interesting in how it turned black! Very cool.

I had something similar happen, but not just a spot. My 25 year old BP when white in a lot of spots. This happened a few months ago, and he has shed since. He didn't gain any of his normal coloration back, but he didn't lose anymore either. I posted here about it, and the feedback I got led me to believe it was due to age, and I have seen it before in other species. This may be completely unrelated to your case, but I thought I'd share. I'd post photos, but my photobucket album is HUGE and it would take me a while to find it..I believe I have photos on his iherp page if you'd like to check him out. He's my only BP, so he's not hard to find.