Peter, thanks for the stack trace. From that, since the crash is occurring in WebKitGTK, it might be the same issue as Bug 750048. I occasionally see something like this as well, and am pretty sure it is indeed a WebKitGTK bug.
If so, you can work around it by selecting a different message that you also want to delete first, then selecting this problematic message, and then deleting them both.
Peter, thanks for the stack trace. From that, since the crash is occurring in WebKitGTK, it might be the same issue as Bug 750048. I occasionally see something like this as well, and am pretty sure it is indeed a WebKitGTK bug.
If so, you can work around it by selecting a different message that you also want to delete first, then selecting this problematic message, and then deleting them both.