Hi there.

I regularly run a mixture of condenser and dynamic mics Including SM58 and similar, on a global phantom powered Behringer and other makes of desk. I can say I have not noticed any issues with changing dynamic microphone responses.

Balanced cable systems are used because they can allow a small wanted signal to be transmitted and received along its length with minimal degradation, and yet large sources of interference can be tolerated and separated from the wanted signal. this applies at both ends of the cable.

The Phantom power is injected onto the cable so it presents as interference (or as a common mode signal), and thus is cancelled out before it reaches either pre-amps, or the sensitive microphone transducer coils. There should be no standing current running through the microphones voice coil, and so should not affect its response.

With regards plugging unbalance plugs in to balanced sockets with phantom power connected, the phantom powering is done through closely matched 6810R (typically)resistors. These provide a current limiting characteristic, and so even if the socket was completely shorted, the phantom power supply will not be damaged.

However care must be taken when using ribbon microphones. Most ribbon microphones will be damaged if they're connected to phantom power sources.

It is always sensible to switch the phantom power system off and allow any stored charge on the supplies capacitors to dissipate before connecting or disconnecting any XLR device.

Possible explanations for any perceived change in microphone performance - there could be many, but I do wonder if the mixer board may have been damaged, such that the DC blocking of the phantom power to the pre-amps has been compromised. This can possibly happen if you hot plug into a live desk.