Maybe related? http://feedback.arma3.com/view.php?id=18849

Possibly, but your issue is when you try running both, might be because of same appid? While my issue is happening with only the Tools.

Now it's happening by running anything, Addon Builder, Terrain Builder, Object Builder, Arma 3 Tools. Nothing makes Steam think it's closed.

Also, running Addon Builder directly from it's directory throws a message that Steam is not running, but there is a fresh launch of it open.

Cant reproduce on windows 8.1 64 pro
Maybe a local steam or admin authority problem ?

Possibly, right now I am just not starting Object Builder through Arma 3 Tools dialog anymore.

Edit: I am running Steam as admin.

Ah right , i think only Publisher is working through : Right click Steam in tool Bar > arma 3 tools > UI > Publisher

all others i think are:
Right click Steam in tool Bar > Name of tool

Hopefully they will leave it so , because last time everything else broke with a Fix lol

I guess, I just made direct shortcuts to all the Tools (except Addon Builder, that wants to be run through Steam for whatever reason).

It started happening again recently so I went mad and went from process to process of those that I didn't know what they were for (or wasn't totally sure), something made it close but I was too fast to see what. When it starts happening again I'll make sure to go slowly and find out.

Happened again, resolved by ending process of Tortoise SVN client, there were 2 of them, once I closed them both Arma 3 Tools responded to Steam that they are closed.

This seems to have been fixed, no more issues since last comment.

Brief explanation: When something is run from Steam, Steam will track and consider every sub-process as part of the launched application. This means that until every process are closed, Steam will still "think" the original app as "Running".

Ticket marked as resolved then ;)