I lost 4 days of editing due to this .. :( ... so now I save a copy of my mission regularly in a completely different folder so I my revert if necessary.

Create a mp 'new editor' mission in the none dev version. Edit it and save it & export it to MP missions ...play on LAN mp... all is ok... any changes you make are saved correctly and mission runs ok.

Now update to the Dev version of the game. Open the previous mission in the MP editor ...edit it and save it .... sometimes it doesn't save ... but sometimes it DOES ! When it has saved you will find that the mission is corrupted and when played will act erratically ...like triggers not working for instance.

Now When you try to save the mission as user save, single player or export to mp missions you get an error message failed to save. Effectively your mission is now corrupted.

If you revert back to the non dev version your mission is still corrupted and still will not save.

I guess the problem here is that if you create a mission in the non dev version and the try to either edit or play it in the dev version the games engine should not allow you to do this ... sometimes it doesn't .... but importantly sometimes it does ... and when it does it corrupts the mission.