Fail to Join WiFi network on iOS6

I updated my iPhone 4S and 3GS to iOS6, and since then I've been unable to connect to my main wifi network at home, that has been working perfectly for years without a hitch. I'm sure this has everything to do with iOS6, as I also have an iPhone 4 with iOS 5 that still works fine like it ever did.

Now, for the relevant data I could gather, that could help Apple support to figure it out or narrow down what might be causing this:

I have a main WiFi router, as well as a secondary one acting as range extender: so, 2 different WiFi networks.

The weird part is: if i reset the iPhone network settings, and then join the main WiFi network, it asks for the password, and joins ok. But the setting doesn't seem to "stick", as if I disable and reenable WiFi again, it doesn't connect automatically to it, and ask for the password again.

As soon as I connect to the secondary WiFi network, the iPhone jumps to it, and this time it remembers it ok - reconnecting instantly after airplane wifi off/on, etc.

But, if I try to connect to the main one after having connected to this one, I always get the "failed to join" error. The only way to connect to it is by forgetting the secondary WiFi network.

With iOS5 all this worked/works ok; so.. I imagine this is some sort of weird bug when using a 2nd WiFi network as repeater/extender. (I'm using WDS)

Also, when trying to connect to the main WiFi after being connected to the extended WiFi (I'm standing right next to the "main" router, 3 feet away, maximum signal strength), the wifi list indicator often keeps turning on both networks at the same time, or jumps back to the second one, while still showing the activity circle connecting on the main one. The thing is, it really seems to be doing something, as the iPhone gets really hot during these tests.

I tried changing the WiFi channels, passwords, checked I had mac filtering disabled, and everything else I could think of. Everything is as it should, and as it always has been... and one can't ignore the fact that a iOS5 iphone keeps working just as it always did, but both iPhones that were upgrade to iOS6 now fail in the exact same way.

So... please Apple, let us get an 6.0.1 WiFi fix update ASAP!