string::PadRight issues

The PadRight() method for strings only seems to work with hard coded numbers.

01 str1 as string value "hello".

01 str2 as string.

set str2 to str1::PadRight(10)   *> this works fine

declare pad as string = 10

set str2 to str1::PadRight(pad)   *> this doesn't work - no trailing spaces in returned string

Am I doing this wrong or is this a bug?