I tried to create a new windows layout for five characters, instead of my usual four. I tried to give it the name "3.1L1R". The next time I logged in, I there was no layout of that name, but there was one called "3"; which I don't remember creating, in fact I have no 3 character setups at this point.

Is the "." character (mis)treated as special?

I've since created a layout called "3+1L1R". Which I can save correctly and refer to later. I can't actually login to play on this configuration, as the EU login servers are having a knap. However I do get 5 windows in the right places, which the right account names in each one.