After testing the biasing scheme for all detectors, two problems emerge.

On the inside pocket, one SiPad (SiPad#3 - Design-I 13) shows a linear current response to bias.
Attachment 1 shows a bias "curve" for this detector 0-60V and a clear linear response for both +ve and -ve applied bias.
This is not a diode.
After extensive testing, no clear problem is identified and no clear solution. 
Possibly some bond wire has popped and there is a short.
All other detectors bias as expected with reasonable leakage currents.

On the outside pocket, SiPad#4 (MSPAD 16A) also does not display diode-like bias response.
Attachment 2 shows the bias response of this detector for both positive and negative applied biases.