This has been discussed before and it is easily misunderstood as a "low remote battery" issue, but that's not the case. I suppose I've noticed this for several months but much more so with the latest software load.
My 501 will get in a mode where it does not respond quickly to the remote. Usually, you'll hit the buttons a few times and it eventually comes up so it behaves like a low battery.
However, with some testing I've found that the receiver is actually taking a very Loooooooooonnnng time to process the commands. When its in this mode, for instance, I'll hit channel up twice and then guide. Nothing will happen. Then about 10 seconds later the channel will change. Another 10 seconds...changes again...another 10 seconds or more...guide pops up.
This will continue for a while. If I leave the unit alone it will sometimes recover on its own, but I usually have to POWER-button RESET to restore normal operation.
Try this the next time you think your remote batteries are low.
Anyway else see this?