(In reply to Anje from comment #8)
The mails are not marked as read.
I agree this occurs...BUT
Note: R is used to mark 'thread as read'.
As I am using 'unthreaded', pressing R would not work.
If a single unread mail is selected, then pressing "R" reliably marks that mail as read. After all an individual mail is just a thread of size 1. I'd expect that behavior to scale to selections of multiple individual mails. That is I'd expect that pressing "r" while selecting multiple mails, effectively applies "r" to each individual mail/thread in the selection. This expectation matches the behavior in TB 102. (One could argue that it's "mark thread as read" not "mark thread(s) as read" but that would be inconsistent with other shortcuts that work on multiple mails)
However, with TB 115 in most cases (I'll get to that in a moment), pressing "r" only has an effect if the topmost mail/thread is unread/contains an unread mail. As a result, marking all currently selected mails as read either requires manually marking the first mail as unread and pressing "r", or pressing "m" twice. Neither behavior is intuitive.
To make matters more confusing, sometimes while I'm in the inbox folder, pressing "r" seems to be applied to individual mails a expected. However, this is coupled with the effect that pressing "m" now applies to each mail individually. That is, if some mails are read and some unread, then the status of each mail is toggled individually. Switching to a different folder returns to the behavior that each mail in the selection is consistently set to read / unread and then the toggling applies to each selected mail the same way.
So I guess I'll have to amend the initial report again (sorry):
Steps to reproduce:
Switch to a folder (not the Inbox !) that is set to threaded. Then select mails that belong to different independent threads. That is, for my scenario just grab 2 or 3 independent mails from different threads (or simpler: just 3 individual mails without any threads). Make sure that all these mails are unread. Then clicking on the first of these mails marks that mail as read. Extend the selection to include all mails.
The resulting state is shown in tb-unread-mails.png . Now, pressing "r" doesn't have any effect.
After manually marking the first mail as unread such that all mails are unread (while keeping the selection), pressing "r" marks all mails as read.
I can select a random set of mails, press "r" and afterwards each selected mail/thread is marked as read, without any regard to the previous status of the selected mails. While in the unthreaded view, each mail should be treated as a thread of size 1, such that the shortcut also works there.