This issue has been circulating for quite some time now.  I originally logged it
a copy years ago.  
1.  Printing envelopes on a KX-P7110 Panasonic printer does not work.
2.  This printer and printers I've owned in the past were and are center loaders
when it comes to printing envelopes.
3.  In the print feature one selects the CENTER position for which to print the
label onto the envelope.
4.  The result has been and still is that the labels do not print even close to
the proper position.
5.  When using OO to jockey the position of the text around the results are
still wrong.
6.  Suggest someone seriously take a look at this feature and test it on more
then just a high end printer which may be the case.  Many of the lower end
printers such as Brother - HP - and Panasonic are center loaders that support
PL6 printing specifications.
7.  The reason I right is that I have received several emails from others who
seem to have found the same issue I had found 2 years ago and it does not seem
to have improved much.

Sincerely,
Concerned OO user