I have noticed this several times now, and is still present in Beta 020.
When I compile a piece of my project on its own pdf file, nothing happens if the file is open in a reader, even in Win7 Explorer window.
Nothing gives me an information that the file cannot be overwritten.
I’m prompted to overwrite, but when I open the pdf file, it has still as many pages as before.
And it is only selected in Windows explorer, with the viewer panel open…
Could there be a dialog telling when compile function will not proceed?