When a user is in an IRC channel, they can accidentally modify the topic of the channel. Not what the channel's topic actually is, but just what is displayed as the topic for the user.
For example, If I click in the topic field, I can just start deleting things from the topic. I discovered this when I accidentally deleted part of a topic containing a URL. Sure enough, I had deleted a character from it, but didn't realize that I had mangled the URL.
Steps to Reproduce:
1. Join an IRC channel
2. Click on the Topic
3. Insert / Delete characters
The topic that displayed was affected by the insertions/deletions.
The user probably shouldn't be able to modify the topic in this way.
Please file this as an RFE upstream.