I was playing through the game as normal, and ended up discovering plasma tech before I had researched heavy lasers, so I decided to skip straight to plasma. Further on in the game, when I had reached MAG weaponry, I decided to research heavy lasers so my scientists weren't sitting there doing nothing. However doing this replaced the MAG defences I had built within my base with Laser versions, which was a downgrade. So far I have found no way to fix this as it replaces the option to build MAG defences with laser ones. This is easily reproducible.
Screenshots of bug included.