Switching Polar Patterns With Phantom Power Enabled

[iangomes]

I did a search and couldn't find anything. I bought a pair of MG UM70S's, and found that the back capsule did not work on figure 8 pattern (but did work on omni). I spoke with the seller, who was very helpful, and he suggested not changing polar patterns with the phantom power enabled. I had never heard of this and couldn't find anything about it. I retried the microphone, and the back capsule worked perfectly in all polar patterns. I couldn't even recreate the problem switching polar patterns.
Is there danger in this? I understand that there may be problems plugging in microphones with the +48 on (which I may have done the first time). What is the science behind these issues?
Thanks
Ian