[TYPO3] Foreign url injection?

[Logi Huldar Gunnlaugsson]

Hi list,

I have this interesting (and extremely annoying) problem with one of my
websites. Every now and then a foreign URL is injected into a link (both
menu and links in content). The site is multi-language and url use the
&L= parameter. I can browse the web and every thing is OK but then I
click a link (any random link) and this gets put in the language
parameter of the site:
http%3A%2F%2Fbusca.uol.com.br%2Fuol%2Findex.html%3F (or:
http://busca.uol.com.br/uol/index.html/). Every link will use that
parameter there after (Typo3 thinking that this is a legitimate
L-parameter perhaps?) but the links work just the same. Now, if I clear
the FE cache everything returns to normal until the url is injected
again into my cache. 

Although I've never seen anything like this before I guess this must be
a problem that people are experiencing all over. The thing is also that
I have no idea what this is called so when I try to google the problem I
get no intelligent results.

Can anyone out there help me or point me in the right direction?

Cheers,
Logi