Version:           1.0.1-4ubuntu2 (using KDE 4.0.2)
Installed from:    Ubuntu Packages
OS:                Linux

Repost of <https://bugs.launchpad.net/ubuntu/+source/konversation/+bug/194423>:

Binary package hint: konversation

DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=8.04
DISTRIB_CODENAME=hardy
DISTRIB_DESCRIPTION="Ubuntu hardy (development branch)"

Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Installed/Config-f/Unpacked/Failed-cfg/Half-inst/t-aWait/T-pend
|/ Err?=(none)/Hold/Reinst-required/X=both-problems (Status,Err: uppercase=bad)
||/ Name Version Beschreibung
+++-================================================-===================================-======================================================
ii konversation 1.0.1-4ubuntu2 user friendly Internet Relay Chat (IRC) client for KDE

If you click on a nickname containing a backslash (let us use "test\test" as an example) and e. g. try to whois the user using the UI, the backslash is silently converted to a forward slash (so the actual nick whoised is "test/test"), so the whois either fails or possibly shows information about the wrong user.
Directly using "/whois test\test" works, though.

This bug could apply to more UI functions than just whois, I just did not test any.