It would seem that a bug has been introduced.
Playing skirmish mode, when I go to the design screen and try to change a design the design rarely 'sticks'. Although I can change it on the right it is (rarely) echoed on the left hand side (list of existing designs) and if I change to another screen (say manufacturing) it now loses the new design. Now and again it works, seems to be no rhyme or reason.
Not had this problem before 2.3.7. If I create a completely new design it works fine (but slow and a pain).
Update: I have tried to re-create this but failed! Seems to be in one particular game (and saved game) on map SK-Urban-Chaos-T1 but have been unable to re-create it so far. Will try again at some stage with exact same settings (if I can work out what these were).