After spending 40+ hours in Forge I have come across several bugs and issues that need to be addressed:
Shifting objects - I have heard of this happening but never experienced it until a few days ago. I normally forge alone but this time I let my friend in the game to tweak a few things for testing. I noticed after the next playtest that some objects were not lined up and when I went back into forge I noticed that everything (yes EVERYTHING) had shifted +/-1 degree on the yaw. I spent about 90 minutes grabbing every piece and fixing it, but it should never happen. My guess is that my friend was given host while I forged and saved on my map, and that somehow messed up the coordinates. This is a serious issue that needs fixing.
Trait zone default - I noticed early on that if you failed to alter a setting in the trait zone to “unchanged” it will give the player default traits. So, for example, if you set up a gametype with bottomless clip and then put a trait zone to give the player invisibility they will lose bottomless clip unless you also set that parameter for the trait zone. Problem is that if you set the trait zone to unchanged it changes back to the default setting after you leave, essentially making it impossible to use trait zones with custom gametypes unless both have the same setting. If you set up a trait zone to work for default gametypes it will not work for customs and vice versa.
Lastly, if you try to place/grab very large objects (namely Silo 3 on Impact), or try to work in very tight areas your character moves and can get stuck in walls or flung off the map. Not to mention it can sometimes alter the position of the object you were holding. Please just remove any and all movement when interacting with objects, the game feels really buggy when it happens.
These are all pretty serious issues and I hope 343i will fix them. 1 and 2 especially.