When using the ALT+CTRL+ESC sequence to break into kdb, the keyboard is completely borked when you return. watch(8) shows that it's working, but it's inserting escape sequences.
Further investigation revealed that VT_ALT_TO_ESC_HACK is the default and directly conflicts with this sequence, so upon return from the debugger ALKED is set.
Let's just assume that they didn't mean to trigger ALKED if they broke into the debugger, because it's certainly surprising.