Hi Adam,
I solved the problem! Perhaps it was a mistake of mine but I thought it could be considered as a minor bug too.
The problem probably not raise frequently (almost never I guess) because it happens on pages with two or more C.E. with different CustomCulture sets or one set and the other not and vice-versa.
I'll found that doing myself a little debugging on the code; if you like I can e-mail you where I found the problem but I'm sure now you have already understood all.
Thanks anyway
Nicola