No bugs here. Both of these work as expected. I think the issue is
you're confused about font-lock-mode and text properties. These are
not the same thing. Font-lock-mode is just one way to add text
properties to text, so may other functions. Deactivating
font-lock-mode does not remove all text properties, only on text with
the `(fontified . t)' property. This is why you're seeing what you're
seeing.
Please explain this to Stefan M, who considers this to be bugs, who
would like to deprecate the font-lock-fontify-{buffer,block} commands,
and who guided me to write the font-lock-update command.
For sure. If you can, please link me to the lists.gnu.org message?