If I test with the phone using my thumb to cover the sensor, the screen turns back on after some seconds. Attached is a logcat of this.
Defy+, CM7.2
Thanks for providing the logcat. I checked it out and it seems that (for some reason) the proximity sensor is actually being triggered again and as a result, the Screen On function gets fired. I'm not sure if this'll make much sense but I'll give it my best.
The proximity sensor is triggered and the screen is locked using Android's in-built functions (i.e. so far so good, works till here) and then only a few milliseconds later the proximity sensor thinks your thumb has moved away and only then the Screen On function is triggered (there's no other way this function can be triggered) using a "wake lock" (Happens in the log at time 00:26:51.835).
So the bottom line is, all the evidence points to the fact that it's a physical thing BUT I'm not sure if it's a hardware thing. For example, sometimes if you press down on the proximity sensor, the detection won't work, so try hovering your thumb just a little bit above the sensor, or try using a cloth. It's a pretty new and buggy technology so I'm still figuring it out but yes, there have been maybe half a dozen other reports of the same issue, so you're not alone. Unfortunately, half a dozen out of 5.5k+ downloads is not conclusive enough to find the root of the issue and the log doesn't reveal any issues with the app.
So basically just try testing with a few different scenarios, and although I'll keep trying to look for some concrete reason, if it still doesn't work, I'm sorta stumped right now. >.<