Redirect bug when mass-hiding comments

[TSP]

I'm really struggling here. The issue is that I'm able to reproduce it in one environment, but not in the other. Both environments are pretty much equal. 

If a topic title contains a norwegian letter, like æ, ø or å, then when I select posts with the checkbox and choose "Hide" in the options, it redirects to the following error message: 

Sorry, there is a problem
We could not locate the item you are trying to view.
Error code: 2F173/I

However, that does not happen when the title does not contain a norwegian letter. 

Thing is.. this issue is on one installation and not the other. They both use furls and on the same IPS version. I can't figure out what's different. 

Any ideas or can anyone else reproduce this?