When using

testfor @p[score_deaths]

or

testfor @p[score_deaths_min]

in a command block, it doesn't output a redstone signal when adjacent to a comparator (assuming the condition is true)

– Fixed – --New Bug –

When using a comparator clock, and the redstone input is within about 3 blocks of the comparator, the command block (or any peripheral) will not receive redstone activation.