As far as multiple short names not working, I'm not totally surprised. Sorry I had not considered it as a notice in the article somehow. The reason it does not work with multiple short names is because procmail attempts to deliver mail to a specific mailbox. When you create multiple shortnames for a user account, only a single mailbox is made, which has the name of the first shortname used. When procmail attempts to deliver to one of these alternate names, it can't resolve the name properly because its box doesn't exist.

I'm not sure how you're using the shortnames. I haven't found a practical use for them in my organization's server. However, if you're just using them for aliases to the same mailbox, you should be able to modify Postfix's /etc/aliases file (and then run newaliases) to create aliases for the mailbox. The aliases should work properly with the above described config, since the resolution of the alias occurs prior to the pipe to Procmail.