There is a .thumbnail folder inside of the DCIM folder on the SD card, plug your phone into the PC and view as a usb drive... go in and delete the pictures from the thumbnail. You can delete the entire folder and when you access the gallery again it will repopulate again, but it may take a bit depending on the amount of pics you have.
I am getting the same. My phone keeps giving me a warning that space is getting filled but I have already deleted all the files. Yet on the phone the gallery and albums are there. The options on the phone are only to share and get details.