Hi
I can't say why the buttons (and space bar) are behaving as you say they are but as Borate says, it's not how they should behave. I have tried to get VP to respond as you describe and all the controls work as they should whatever combination of keys I use, speed I click at and irrespective of any positions of the cursor lines.
So....Do you have the vpsetup.exe file from your original download?
As you say a fresh download has corrected the problem (for a time), I would suggest that as an interim measure, or until NCH respond, you simply keep the vpsetup.exe icon handy, say, on the desktop. When the error starts to occur save your project and double click the setup icon.
This will simply reload and overwrite the copy you have with a fresh copy of VP which should then work again OK. It only takes a few seconds to reset the program in this way and you can then reload your project file (the .vpj file) and continue. I can swap between versions by doing this and haven't found it necessary to uninstall the software or download anything new.
It might be useful also to send in a bug report.
Nat