Do HA Fillers leave permanent residue?

I've read on various occasions that HA fillers leave a permanent grey, 'slushy' residue in the face. This has come up in discussions about women who've had multiple HA filler treatments, and then undergo a face lift. Apparently when the surgeon performs the face lift procedure they are able to see HA filler residue. Is this true, given that HA fillers supposedly dissolve completely over time as they're naturally absorbed by the body?