When printing envelopes from an address database the application automaticlly inserts a blank page.  

When a file with address database fields is printed, a dialog comes up "Your document contains address database fields, do you want to print a form letter? Yes, No, Help" 

If you select the NO option you can print one envelope and on the OPENOFFICE.ORG tab their is a radio button to stop print of the second page.

If you select the YES option a mail merge screen opens and allows you to use a database as input and print to a file as a single document.  After every document it prints using the database a blank document is inserted automatically.  In selection of the mail merge option there appears to be no way to turn off the automatic insertion of the second page as their is with the NO option. Users have a great need for the ability to turn-off the blank page insertion because without it we get a print file with one addressed envelope then a blank envelope then another another addressed, and so on.