Version:           1.11.3 (using KDE 4.2.3)
OS:                Linux
Installed from:    Slackware Packages

Please see the attachment while reading this report.
"Today" is Sunday, and I have this rather long thread, which spans across multiple days. Because the latest message in it was on "Friday", the group in the message list displays "Péntek" (which is Friday, in Hungarian).You see, the last message on the bottom is dated May 29 (which was Friday). The previous message displays "Today", and the message before that displays "Yesterday" and so on, but those are wrong, beacuse they display these "relative" dates according to Friday (what is the day on the group header in the message list). The message which says "Yesterday" is dated "Thursday" (which is yesterday according to Friday), and the message which says "Today" is dated "Friday" (which is today according to Friday), but today is Sunday.
So I think there is some inconsistency regarding to message dates.