Did you find this here...
http://www.coramchambers.co.uk/MH_Paper.htm
Is it definitely a Form A, I have to admit, I'd go for a Form N to stop this happening.
Why have they gone for a Form A as usually it's for tenants in common to protect both their interests.
It is involved in matrimonial or separation proceedings, ie a former partner not on the register wanted to get their share of equity if sold?
If you're trying to avoid someone getting their share then the court may take a dim view depending on the circumstances especially if the court has been involved to date.
I'm guessing you're looking at adding someone to the register so you can sell without a court order but this is not what the restriction is usually for from what I can see.
More details on the wording of restrictions here...
http://www1.landregistry.gov.uk/assets/library /documents/lrpg019.pdf