First try replacing setText with sendKeys instead. See if that changes anything.
WebUI.sendKeys(findTestObject('input_PostalCode'), '61701')
I remember there was another OP that had an issue with entering numbers into a textbox and I believe he had to enter them one at a time, using sendKeys. It was on this forum somewhere. That’s another thing to try. If something like it works, then you can make a Keyword out of it with perhaps a loop and substring() parsing method.
Edit: Here are some other ideas: