OK found only this in the White Paper for a Previous Bug Fix Build for VP12:
"Fixed a bug that could cause image sequences to have black frames in Video Preview and rendered output after zooming in with the Event Pan/Crop plug-in and time compressing."
Aija, Grazie is referring to the release notes of VPro 12. This is supposed to have been fixed before the build you are using though.
See a recent thread on similar issues in VPro 13, if there are some pointers for you there.