Dues Renewal Invoice e-mail ZIP code bugaboo

More subtlety?  On the heels of my recent "Dues Renewal Invoice e-mail ignores DATE LOCALE settings" support request I find another one in the same processing area.  This time it's partly my fault (so much for the suggested pay raise).  For jurisdictional issues I won't get into I put the ZIP code in the "Mailing address for check [ADDRESS]:" field in brackets: [19446].  That shows up properly on the Dues Management Invoice Preview tab (screen shot 1, attached), but the PHP (?) code that generates the e-mail, when examining the ZIP code value, appears to, rather than simply using what's there, or perhaps eliminating anything other than digit characters, is tossing the whole shebang (screen shot 2, attached).  Since I'm working on a REGEX issue on another site to properly allow phone number field entries, this type of matter is at the top of my mind.