put a command-block with a testfor command, make the command 'true' and put a comparator nest to it facing outside, use a button to power the command-block and the comparator and his further redstone output will stay powered for ever, maybe not a bug, bug its REAALY making it hard to do things with it. i suggest it will let through the signal and not make is endless powered untill its powered again and the command is 'false'