What?? Wait!! What is that? I'm agreeing with [MENTION=348133]panzerwagen[/MENTION] that this split is from the stem expander, however, it looks like there are no threads in just that area but are around the rest of the steerer tube. That area also looks to be painted rather than bare metal.

Was this section of the steerer tube indented, which would be why it didn't get threaded and then got painted? Then being indented, cracked when the stem expander was tightened?

Can we get a few more pictures from different angles. This sure is odd.