Glue the mitered return in place with a fast-acting cyanoacrylate glue formulated for wood (Krazy Glue is one brand). The post 6 Tips for Perfect Trim on Doors, Windows and Base Moldings appeared ...
Windows are custom-built ... So, they brought the wood. They then put my own trim back up to modify it for the inside of the French doors. They were punctual. They were very nice and polite.