FWIW - Found this in the LR Baggs MixPro manual:
"4.2 Crosstalk: Crosstalk is interference or "bleed" between two signals within a common shield, such as a stereo guitar cable. This common
problem is often encountered when a high-impedance piezo pickup is mixed with a low-impedance active source, such as a mini-mic. The bleed
signal from the mic mixes in the cord with the pickup signal and appears in the pickup channel. The higher the amount of amplification (gain)
required for the pickup (and longer the cable), the more of the mic signal will be present in the pickup channel. It is common to encounter 25% to
50% mic bleed into a clean pickup channel."
The mag pickup signal isn't active and is probably higher impedance than a mic, but I'm sure it's a lot lower impedance than the piezo.