Deep well pump kicks in at 35 PSI and drops to "0" PSI - what's going on?

I had a new deep well pump and bladder tank just installed. The pressure switch is set between 35 - 50 PSI and seems to work fine - the problem occurs when the pressure drops to 35 PSI, the pump kicks on, but the pressure drops to zero instantly for a second or two before the pump can build up pressure. It almost seems like a check valve is missing or something.
I'd like to get a little knowledge of the situation before calling the plumber who installed it.

Thanks

The precharge on the bladder tank is too high. Calibrate your air pressure gauge with your water pressure gauge.