Me and my borther where playing together and can not shot each other on the normal factorio world.
In the Blueprint Lab we can damage each other, looks like it is somehow reversed.

-ups i did not categorized it as bug, will create another another post so the other on is duplicated

It looks like every time you enter and leave the Lab you get invincible, even in singleplayer

Crap. I renamed some variables to be more clear on what they were because the original dev didn't have them super clear and i kept mixing them up. Apparently, renamed the one that handles lab character invincibility to the affect the non-lab character when renaming the variables. Sorry about that, I'll get this fixed up shortly.

Since this isn't something I can handle in migrations (offline players characters don't exist to the modding api) I'll have to set it to fix this whenever you leave the lab. So the next time you enter the lab and leave again everything should be back to working correctly.