When deleting a message Akregator selects the message above the deleted one. This is the opposite of the usual moving down to the next object, e.g. deleting a message in Thunderbird moves down (more extreme: pressing delete in text editor will keep deleting letters from the right of the cursor).
I can confirm this, Kontact 5.3.0 (QtWebEngine), openSUSE Leap 42.2.
And also in Kontact 5.5.2 openSUSE Leap 42.3.