Locking out the frequency (or putting it in as a conventional channel) won't work, because if the conversation being followed happens to land on that frequency, you will lose it.
Keep in mind that most of the newer scanners default to CC only when doing P25 trunking. The problem, as ngel has surmised, is very likely due to simulcast distortion. There are a couple of possibilities, each related to his RF environment. It may be necessary to add the attenuator to the TSYS definition, or use a different site, possibly with a directional array, like a yagi (very small and cheap, and I'm making an assumption here that the 106 is being used in a home when this occurs)
The good folks in our Florida forum
might have other, more practical answers....Mike