When compiling a project using 1.1.17 of the VS add on I get the warning:
"Build must be stopped before the project can be closed"

Disabling the add on removes the warning.

What I've found is that if the MocDirectory is ./Generated and the Rcc and Uic Directory are ./GeneratedFiles it will create this error condition. I made all the folder locations match and the problem went away.

Something to ponder on a slow day....