no it's no bug but not sure about that if it's has to be like that ,look at the titan skill description it said generate 50 titan ire stacks end of titan stance and side note
"generate 50 titan ire stacks when Dire fist unused during Titan stance"
so it means you can 2 max combo just like that but get no 50 titan ire
but if you do 1 full combo and don't do or fail the 2nd one you can generate 50 titan ire. got the badge also good burst but still need tweeking on rotation.