We don't do many Simrad setups, but do install many Garmin and Hummingbird MFDs. It is common for MFDs to read a slightly different voltage. Anything 0.5v and under is nothing to worry about. As always, the voltages you see on the scan tool and DMM are all that really matter.
I have long felt that some of these problems are due to something going wrong during rigging at the factory. The trouble is that these glitches pretty much require a highly trained tech, a Mercury dealer only scan tool and the possibility of a lot of hours. Only 2 out of the many dealers I've worked for would even think of doing this on a boat they sold. Because at this point it's really only a glitch ---- the boat still boats.