I ran some tests with Felgo on a Win 8.1 VM, especially for the Qt WS demo. Unfortunately I am unable to reproduce the issue, the application does not freeze and runs fine.
This issue probably happens only for your specific VM / Windows / Felgo setup. You can try to build and run the application from Qt Creator with Debugging features, to maybe get a hint for the reason of the freeze.
Otherwise, I recommend to simply use Felgo without a virtual machine on a usual setup.