Windows 8.1 Locking FLAC Files

I am a big music collector, and have never had any issues with my PC and audio. I am using Windows 8.1 and for months things have worked great. My chosen audio is ALWAYS MP3 320kbps as I find it much more flexible than FLAC, and can barely notice the difference in quality so it works well for me.

Normally when I download FLAC files, I run them through a program called Goldwave (an app I have used for years) and convert them to MP3 320, I tell Goldwave to delete the FLAC files once conversion is complete.

I noticed recently that the FLAC files are not being deleted, problem with Goldwave I thought, but on further inspection, I cannot delete FLAC files within Windows Explorer!!

It says I need permission to delete them, even though I am Windows 8.1 administrator. When I right click a FLAC file, the delete and rename part has a UAC shield next to the text. Strange thing is, if I leave the FLAC file along for about 5 minutes, the shields vanish, and I am able to delete, why is this happening?

I previously messed around with UAC settings, but nothing has worked, when the shields display in the right click menu, I try an app called Unlocker, and even this wont delete them. This is ONLY happening with FLAC files, what's gripping onto these files? How I find out? And stop it.