I don't know whether it relates to your case or not, but I have a similar issue which I "fixed" with a workaround. I would open a PDF file in browser and when

I don't know whether it relates to your case or not, but I have a similar issue which I "fixed" with a workaround. I would open a PDF file in browser and when the Downloads window would open, I would right-click on it to clear the downloaded files from download list, not to permanently erase them! As soon as I do so and close the entire window, it would delete the files from Downloads too! My workaround was to change the default Action to Save File and that would be it; the same aforementioned steps do not erase the files from Download folder.