In Heart of the Swarm they're rearranged many buttons for Zerg players, who are using GRID hotkey scheme, and it required to adopt to new layout. Well, one of bad things was a merged Burrow/Cancel commands into one.
I've rebinded Burrow to F1 and always used Cancel command as Escape, sometimes required that hotkey as "B"
Haven't tested it in WOL, but it works well in HOTS, just go to \Documents\StarCraft II Beta\Accounts\<numbers>\Hotkeys\ and open your custom hotkey-file with Notepad. Then find your hotkey command and with , add a new hotkey. Here on the picture above I now can Cancel buildings with Escape and burrow units with F1 or B.
It may help you, because there is no option "Allow hotkey conflicts" for Grid-users. This is a solution: just use 3+ hotkeys on one command.