The switch statement will most likely create a
call to a library with a jump table just behind
that call. Then MOVC instructions are used to
access this table to calculate/find the address
to jump to.

However, I do not know what this has to do with
the protection. You may verify a problem with
MOVC by a small test: create an const array in
code memory and access it, that will also use
MOVC instructions, check if that works.

Best regards
j. christoph