BBcode URL Links to IDN-domains with Umlauts posted by users will result in undesired behavior of the software and in PHP errors.

Our board derräuchertreff.de is ID coded as xn–derruchertreff.8hb.de.

When a user wants to post link to another post within such forum, it looks like:

[url=http://derräuchertreff.de/viewtopic.php?f=40&t=1508]Link to something[/url]

This will not work and create the described problem.
However using:

[url=/viewtopic.php?f=40&t=1508]Link to something[/url]

will work perfectly in that forum.

This problem came with the update from 3.1.10 to 3.2.x and did not exist in 3.1.10 to the best of my knowledge. This is the case for 3.2.0 to 3.2.2