OBS: higher CPU usage in game when obs is running

Question

I'm experiencing a weird issue with OBS, where having it running will cause a game (in this case Colobot) to use more CPU, in my case ~10-15% (it ends up going over 100%, which noticeably degrades performance in this single-threaded game). The interesting part is that usage goes up when OBS is merely running, it doesn't matter whether I'm streaming or recording, preview is enabled or what sources are active. I've tried running a compositor thinking it's caused by obs grabbing contents of windows (compton), but it had no effect on performance whatsoever.

I'd understand if my performance problems were related to CPU being hammered with OBS encoding video, but other CPU threads have plenty of resources left.

Does anyone know what exactly is causing this issue and how to mitigate the resulting performance drop?

I have no idea what exactly causes this, and I can provide more info if needed. I have no clue whether this is a bug or something.

Specs (in case this helps):

• i7-3720QM
• 16 GiB RAM, DDR3L-1600MHz
• Intel HD 4000 (integrated)

My streaming/recording target is 900p60 (software encoding), which peaks at ~40% total CPU usage in worst cases, which should leave enough resources to run the game.