Ha, found & fixed the problem!
The global parameter 34 was set to Poly800, not EX800.
34 GL xx - Device type
xx - 0=Poly-800 MK1, 1=EX800, 2=Poly-800 MK2
This parameter must be set according to the type of Poly-800 unit that the HAWK-800 kit is installed in. For the Poly-800MK1 this parameter should be set to zero. For the EX-800 this parameter should be set to one. In the case of the EX-800,pitch bend control messages and the pitch of the unit itself will not work correctly if this parameter is not set to one.