The current regexp is too permissive, so it will match strings that should not be valid postal codes by themselves
This is caused by a missing "Start of String" and "End of String" anchors in the current Regexp, where it currently rather checks for a word boundary:

\b(?!(\d)\1{3})[13-9]{4}[1346-9][013-9]{5}\b

This results in the following strings being passed as valid postalcodes:

• test123 4351666456 test456
• this should not be 5614736867 a valid post code

PR with a fix is coming in a few moments