It is not a glitch, if you wear kung fu beard with spikeys only 2 spikes show.
It's just certain hair doesn't go with the kung fu beard. Some hair will show, some won't.
Like minihawk will not go with catears, but spikeys will.
There's a limit to how many "hair parts" can be displayed. It also depends on which part ID is used in the hair etc. Thus some work together, some don't.
I should note that they're currently not intended to work together.
<Erf> SkulFuk: gf just made a toilet sniffing joke at me
<Erf> i think
<Erf> i think i hate you