Steps to reproduce:
Not sure.

Stack trace:

+ Trace 211699

Other information:
It seems that with 2.24.3, there is a new regression in that at some point evolution will get stuck with "Formatting Message..." in the preview pane and never actually display the message.  Stack trace above is with evolution in this state.

If I double-click a message from the summary pane to open it in it's own window, it will display there.  If I use SHIFT-CTRL-W to open a new evolution window, the message will show formatted in that window's preview pane.  Now here is the interesting part.  If I select a different message in that new evolution window, it will get stuck "Formatting message..." but the previous evolution window will now be showing the message that it was stuck formatting.  If I move to a new message in the old window, it will get stuck formatting but the message in the new window will display.  These two windows will continue to oscillate in this way, each taking turns displaying a message followed by getting stuck formatting a message until the other window displays it's message.

The only real way out of this I have found is to restart evolution.

BTW: have you folks considered releasing what would have been the next 2.22.x as your next 2.24.4?  :-)  It would probably be a lot easier than chasing all these new regressions in 2.24.