Could it be you are running an older version of the game or maybe you haven't installed the latest 3.5 patch before you installed beta4?
I can't seem to replicate this problem ...
I am running a new Beta 4 clean install. - 23 august
Though it is not happening as much now - perhaps if the game was trying to put the officer with the best skills in the most appropriate post since I have got more officers now there is not so much oppertunity for it to happen - and not so many posts to be filled.