The problem was that a shared InnoDB row lock was taken when executing
SELECT statements inside a stored function as a part of a transaction
using REPEATABLE READ. This prevented other transactions from updating
the row.

InnoDB uses multi-versioning and consistent nonlocking reads. SELECTs
should therefore not acquire locks and block other transactions
wishing to do updates.

This bug is no longer repeatable with the changes introduced in the scope
of metadata locking.

Test case added to innodb_mysql.test.