Problems with iMac sleep mode & Spotify

I've had problems with my iMac's sleep mode for some time : Sometimes it takes pretty long (like 10-20 sec or something) to get the computer to sleep mode. More annoying, sometimes the computer wakes up itself after a couple of seconds. But, the problems seem to occur only every now and then, not all the time.

Now I got fed up enough with this and examined things a bit. Short googling didn't help straight but I ended up checking out logs from Console. Spotify seemed to have pretty many log entries there so I ended up closing it. That makes sense, since Spotify's P2P architecture is probably sharing music from it's cache on my computer every now and then.

After that, I haven't had any sleep mode issues at least so far... (went to sleep mode only a couple of times so far). But thought to share it in case somebody ends up googling with similar problems.