This is due to the wip nature of the qtwebengine port. From the changelog:
wip: first version with support for QtWebEngine instead of QtWebKit - some browser based applications, esp. the "notes", do not work as expected yet
Rene never managed to finish the switch. I am probably not going to be able to finish it either, at least not in the short term. Not being able to build for windows under msys is another issue asjus QtWebEngine is based on Chromium which can be only built using msvc on Windows.
Short term I might just create a branch in my fork reverting the QtWebEngine changes, or just delegate them to a separate branch.