Bug with value in custom profile field - text type

I have created a custom profile field of type "simple text field". Options are:

Size of text field: 5
Minimum number of caracters: 1
Maximum number of caracters: 6
Validation of field: any caracter

If I type 0 (zero) I have an error message, which is wrong.
On the profile page, it says "The field “xxx” must be completed."
When completing the field on the registration page, the error msg is different.

Please see http://www.phpbb.com/community/viewtopic.php?f=46&t=1894035 where member HGN gives part of the correction. He also says that : "Even if you select "Only numbers (0-9)" at "Field validation" it does not except a "0"."

Thanks.