Breaks on multilingual sites with a domain per language

Hey there, I currently have a site online in 2 languages, dutch and french, to make things easy, I'll call one domain www.domain1.com and the other www.domain2.com

so, first of all, this is not a multisite, it's 1 site, 1 codebase, fully shared tables, but language depends on domain, domain1 is in the default language (dutch) and domain2 is in secondary language (french)

when I'm on domain1 and I log in and switch to domain2, it seems to seriously malform the url it sends me to
sort of like this:
http://www.domain1.comhttp//www.domain2.com/sharedsignon/.... and so on

so it seems to add the url it wants to go to to the current path, most likely because it strips the ":" from the http://

is there anything I did wrong that caused this, or should I be looking at the source of the module?