I am putting 2 DSS 4450's on a 4424LD+ and they both work but on the second one when you press a button it dials the extension but the light doesn't come on for any extension. If I swap the 2 DSS mods it works fine in the first position still but not the 2nd one so I know both of them work. I can also press intercom *00 and all of the lights on both modules light. Is there something I'm missing? Has anybody ever gotten 2 of them to work properly?