When you double-click on the the sender of a message, the message only opens if the column “From” is large enough to display the hole name.
Same story if you double-click on the subject of a message.
You can bypass the problem by adjusting the column. But I should be nicer if you can just double-click also when the column is to small.
Thank you for reporting, we will fix it immediately.
It is now fixed in our internal builds, it will be available in the next update (probably in a few days). You can workaround this issue to disable tooltips. Just go to Tools->Settings->Appearance and uncheck Use tooltips for overlapping texts.
Thanks for the quick intervention and the work around!