This definitely seems to be an issue when a device (iPhone / iPad) picks up the direct mode SSID and is connected via WiFi, the card has photos to send, but app is listening to connect.
In that mode it doesn't seem to timeout, it just thinks it's transferring when it's not. I think the 5dMkiii prevents auto off when it believes the card is transferring. If the card is simply attempting to find a device to connect to the same thing doesn't occur, it times out according to the direct mode timeout settings for the card.
After that, the camera wait's its own timeout period and powers off.
So I suppose the question is - why does the card keep looking for receivers indefinitely when connected to a network. It seems like it's using the 'am i connected to a network' status to determine if it should timeout or not, rather than 'I have a connection and found a receiver' - such that if it either doesn't get a connection or fails to find a receiver in the timeout period, it should go to sleep.
BTW. this happens even with the direct time-outs set to 4min, not just with indefinitely set.