W52H Number of handsets that ring

[Vitalservice-Kevin]

Hi,

We have a W52P with five W52H handsets attached each of which is successfully registered and was running a relatively new firmware release. We have had a problem with them from day one whereby only four of the five will ever ring when there is an incoming call. We also have a T38GN setup, originally it looked like a restriction on only five phones ringing at one time so it would be four of the W52H's and the T38GN. We changed the routing to exclude the T38GN and the same issue occurs only four of the five W52H's ring, and the odd thing is that it is a different four each time. Does anyone know of a setting which may be causing this? or is this a restriction of the devices?

They are currently running firmware 26.40.0.26 and the base has 25.50.0.20.

Any assistance would be most appreciated.

Thanks
Kevin