I have just completed a trip from the UK to Belgium (and return). SD flight plan submission worked very well on both occasions.
I also successfully added an extra required address (due to the French closed BRIA offices).

However I noticed that my outbound FPL to Belgium had more listed FPL addresses than the equivalent for my return back. Is this normal?
For leaving the UK, the e-mailed confirmation of FPL contained these addresses:
EGKHZTZX EGZYVFRT LFFFZFZX EBBUZFZX EBBRZPZX EBKTZTZX EBSZZRZX LFBDZPZX

For the return only these were listed:
EBBRZPZX LFBDZPZX

LFBDZPZX was the address I added, so for my return flight the only address SD created was EBBRZPZX.
I am surprised that no addresses for UK were included but perhaps the Belgian FPL processing system takes care of that?
Tony Nowak

The Belgian authorities take care of that. In fact, they may object to your adding additional addressees, because they may not be aware you have done it, and they will be sending your flightplan onwards to the French anyway. The French may then end up with two copies of your flightplan.

Thanks Tim for the info.
This was the first occasion I have used SD for FPL submissions so wasn't sure what to expect.
 The additional address I added was as per the French NOTAM regarding closed BRIA offices. For flights to France (and crossing French FIR), for that area, it would usually be Lille BRIA. The NOTAM said to send to Bordeaux BRIA so assumed that would be my responsibility?
Anyway the FPL got to where it had to go!
Tony

Technically it should probably have been the Belgians' responsibility but I would probably have done what you did and add the address myself. Such is the murky world of flightplan addressing.