What aircraft are you using?
I just tested my Saitek Switch Panel with FSUIPC 4.944a and SPAD v0.5.1. In both the default C172 and Carenado C172 all lighting, including panel lights worked as they should.
The panel switch did not funciton correctly with the A2A C172. However, I had not tested this in any prior versions of FSUPIC4, so I can't say that it ever worked. The reason being that I don't do night flights and therefore never use the panel lights.
I did notice that when using "Shift L", which is the FSX keyboard assignment, that the A2A panel lights have two brightnesses, which is certainly non-standard in that the FSX default is either ON or OFF.
If the aircraft you are flying has only one level of brightness, then you can assign the key combination specified in FSX to the switch. My guess that it the switch is presently set to "FSUIPC Offset Change".