Yes they do. If an image is under free art you have to
release any
derivitivies under free art and can't release them under the GFDL.
Thus callinging them compatible is false.
I never said free art was compatible with GFDL. There are licenses
which are compatible (I'm no expert, so I'm not going to try and name
any), those are the only images that can be on Wikipedia that aren't
released (explicitly) until GFDL (excluding fair use).