I don't know what this has to do with Idle Master.

its fixed thx anyways
and it was caused by idlemaster

I just experienced this too. I've been using Idlemaster for a long time, but it's the first time it's ever done this. Every game that I needed idled was not installed. I idled them, and now they all show as installed.
I can't install them because the only option is play.
When I click play, the launch box pops up and disappears right away and nothing else happens.
When I click manage and uninstall, again nothing happens.
When I click manage and browse local files, again nothing happens.
When I click properties and local files, I see the following error - Something went wrong while displaying this content. Refresh. Error referrence: Library_7541554_cfb819666b0ff1fe Cannot read property 'strUserLabel' of undefined.

I'm not going to panic just yet, but this is definitely an error caused by idlemaster. I'll play with it some more and see if I can find a fix.

Ok, I couldn't find a way to fix it through the menues, but after shutting down steam entirely (not just closing application, but killing steam through task manager) and restarting fresh, the offending entries were gone. So it is an issue, but apparently a transient one.