Pre-compressor mist and "apparent" boost reduction

[masterp2]

a number of reports from different sources say that boost readings decrease when WI is activated.

I have my own idea on why this may be, but would like to start a discussion.
It might be helpful to differentiate turbos. Some are wastegated (mechanically work limited) and others are variable geometry with MAP feedback controlling plenum boost (not work limited). Most newer vehicles fall into this category.

What is your explanation?