Just getting on here now, had to catch up on some sleep today. I wanted to point out a few things and answer some of your questions that came up
If a GPU locks-up, its pretty much always caused by an overly aggressive overclock. Smartcoin its self has no role in this at all, it simply launches and shuts down miner profile instances by a set of rules and defined profiles. Also, another thing to realize is that just because "User X" can push their card to a certain limit doesn't always mean that everyone can - small differences such as power supply used, motherboard, cooling method and even slight changes in different revisions of the same exact card model can make possible output vary quite a bit.
Regarding the <<
If the idle message is happening a lot, or appears to be happening in cycles, look at the GPU temperature. Catalyst has its own temperature limiting algorithms, and on most cards they will start throttling themselves and even shutting down for short periods if temperatures go over 90 degrees.