Runic Power Generation bug(?)

I have been leveling a frost DK and started to grab hold of the spec , lately , i have noticed i do not generate Runic Power (VIA Killing Machine procs) after casting Reaper’s Mark on the target which causes frustration when i line up Reaper’s Mark with Pillar of Frost since Runic Power spenders generate KM Procs if you are spec’ed into “Obliteration”

I know we have Empower Rune weapon in our tools should we fall behind in Runic Power but i can’t help getting confused on why sometimes KM Procs does not generate Runic Power , is it a talent i ’am Missing? or a recent bug?