Possibly it has to do with a signal mismatch between the Roku and the TV when it wakes up. In our Comcast cablebox, the TV searches for signal when changing between channels of different signal, i.e., from 480i to 720p, to 1080i channels. That happens when the cablebox is set to output Native signal. To avoid the searching and make channel changing quicker, the box can be set to always output 1080i, the native signal of the TV. Possibly it's something like that. Check the Roku setup menu, or search the forum for a Roku thread if there is one.