What else does sp_addmergefilter do

Question

I am running the following stored procedure to add a merge replication join filter,

sp_addmergefilter

What else does that stored procedure do behind the scenes?

I am calling that stored procedure and in one case it is timing out after 10 minutes. The join filter is this for the two tables DispatchLink and Dispatch,

Dispatch.DispatchId = DispatchLink.DispatchLink1 and Dispatch.ContractId = DispatchLink.ContractLink1
or Dispatch.DispatchId = DispatchLink.DispatchLink2 and Dispatch.ContractId = DispatchLink.ContractLink2

The structure for those two tables is explained here,

How to Optimise Query

If I remove all the stuff after the 'or' it runs fast.