Perhaps there is some other software installed that is conflicting with this.
Perhaps Dropbox and Google Drive both cause the issue... I've never used Dropbox before, but another user had the same issue. I only seem to have this problem when Google Drive is running, so I don't really know.
I had a problem over the weekend, where backup1 was not accessible, and Construct2 said it couldn't rename backup1.tmp to it, and that I should report it... so you're definitely right on that part... but I can't seem to figure out why this happens... as you can see in the video, I can make it happen on command.
Is there no way to add a 'cancel' to the save process? Even a timer, that if it has taken over 2 minutes to save, to come up with a box saying "This save is taking longer than it should... do you wish to cancel?" or something? That way people can double\triple check everything before saving again... or worst case scenario, save in a different directory completely?