Pronto RU980 and Pace NTL box using Red Eye...ghostly happenings...

Hi,
I programmed a Pronto RU980 for a client yesterday. I'm aware of the conflicts that happen using Pronto's and NTL boxes, but was under the (false ) impression that this problem had been solved with the Di4000n box.
Here's what's happening...

The Pronto sends the code (I know this because there is a remote eye feeding the rest of the equipment in the cupboard - it blinks when the Pronto is activated...), but the NTL box does nothing...however, 30 seconds later (sometimes even a minute!!!), the NTL box will react to the code and change the channel.
It will only stay on that channel for a couple of seconds however - it then goes to channel 7 or 0, WITHOUT the remote sending it a command to do so...
The remote receiver in the box is fine, as, with the red eye removed, it reacts immediatly to all it's commands...

Anybody have any experience of this...or even the solution...?

Many Thanks.