Unable to use "case" command on Grub shell; getting syntax errors

[xtec]

Hello.
Using Grub 2.06

I'm trying something simple like this:
str1=abcdef; case $str1 in a*f) echo yes ;; esac

But, regardless of how I split the command, I always get this errors:
error: ../../grub-core/script/lexer.c:352:Syntax error
error: ../../grub-core/script/lexer.c:352:Incorrect command

Even just typing "case" and hitting Enter.

Other constructs such as test, if, for, do work normally.

What am I doing wrong? Can someone help please?
Thanks.