%opt [ $+ %temp1 ] = %temp2
echo @Status 10 $+ SET -> opt $+ %temp1 = %opt [ $+ %temp1 ]
should be
%opt [ $+ [ %temp1 ] ] = %temp2
echo @Status 10 $+ SET -> opt $+ %temp1 = $eval($+(%,opt,%temp1),2)

Spelling mistakes, grammatical errors, and stupid comments are intentional.