asterisk users - Feb 2006 - HELP, SPA-2002 - SPA-2002 singleside sound

Hi,

I have the folowing setup

SPA-2002 (exten 22) with a Motorola ME4052 dect
         |
Asterisk 1.2
         |
SPA-2002 (exten 58) with a Motorola ME4052 dect

All connected to a simple switched lan.

When making calls, sometimes the incoming (58) side does not seem to be 
capable to send voice data back to the outbound (22) side.

Setting reinvite to no, does not seem to help much (on the asterisk side 
traffic seems to flow in both directions according to show channel xx).

Detail can be found on http://nat1.sipman.net/help
Questions:
1. Is this a known bug (I am using version 3.1.5)
2. Is there a workaround to these kind of problems?

Hope anyone can help.

Bernard