GRANT EXECUTE not working 5.1.30?

[Van Stokes]

MySQL 5.1.30 x64 on Vista SP1 x64.

We use MySQL Workbench SE 5.0.29 to generate our schema. The schema has stored functions and procedures. We confirmed that we did set the EXECUTE privilege to the user group for these procedures. We confirmed it by reviewing the forward engineering script and the following statement is present (copy and pasted from WB):

grant EXECUTE on procedure `mytest`.`MyProcedure` to OS1001;

That statement never sets the execute permission (root is running the command). If we run the command manually (i.e. via MySQL Query Browser) it also doesn't work. However, we can set the EXECUTE permission via MySQL Administrator.

So, why doesn't the above statement work?