Save As just writes the VPJ instruction file that tells the project what to do. Save Project File AS routinely, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite. From the HOME tab, that choice is available by clicking the chevron to the right of the Save Project button on the toolbar.
Export, on the other hand, creates a playable video file, such as mp4, avi, mov.
The issue you mention may have been fixed. Install the latest release. For licensed users upgrades are free for up to six months from purchase date. After that, VP will continue to fully function but a fee will be required in order to register the newest. Retain your old install file and registration info.
Report back if you see the split-screen again.