Hi. I'm not sure if this is a bug, but it happened to me right here on phpBB.com.

The problem is this: If a user with no permissions to use topic icons, edit his message, then the topic icon is lost.

It happened to me with a topic of mine which had a "solved" topic icon set by a moderator, and I edited the topic to add "[Solved]" to the subject line, then the topic icon was lost. (Moderator's probably pissed with me right now, he-he!)

Again, I don't know if this qualifies as a bug.