Groups don't appear when re-welding a blueprint on the same grid
Make a simple grid with functional blocks, put them in Groups, add some armor blocks sticking out to be grinded when print finishes. Make a blueprint of it, then create a printer for it. (I had a large grid with welders and rotor-based conversion to small grid, with projector on the small grid, but size shouldn't matter.) The first time the printer welds the blueprint, the Groups appear as they should. Then grind of the connection between the projector and the blueprint and have it print it again. The Groups do not appear this time. If you use merge blocks to disconnect the welded blueprint, same problem happens.