I periodicaly upgrade my constructors with more/faster engines.  Version 2  of the constructor had a 4 speed. Version 3 had a 9 speed.  Next version had a 19 speed. I upgraded all of my my version 2 and version 3s to version 4.  When upgrading finished I sent my constructors off to quick build a starbase.  That's when I noticed that they were only moving 4 spaces.  I check them all and see that they now have 4/4 or 5/5 for movement.  I then produce version 4 on some planets and see that after I launch them that they have movement of 19/4 and sometime 19/5.  After the initial 19 is used these constructors now move at 4/4 or 5/5 like the upgraded ones did. 
Any one see this before?