Comment 11 for bug 1152490

Same problem here. I noticed that the number of unread messages does not appear on the affected machine.

I have another Ubuntu 13.04 (upgrade from 12.10) running at my work PC at university not experiencing the problem and showing the number of unread messages. To exclude possible problems with the Thunderbird account I copied over the whole account from university. No change, the very same Thunderbird account runs flawless on the University machine, while the symptoms appear on the laptop at home. So it must be some external factor.