EF6 - unpredictable results with adding a table (epic time waster)

I have a SQL Compact db with about 40 tables or so, and an EF model.

Two of those tables are A and B. I want to add a junction table AB.

In the SQL Compact toolbox I delete the relationships between A and B and create relationships between  A and AB as well as AB and B.

From  this point forward things never seem to work correctly.

I open up Model.edmx and delete the relationship between A and B from the model. Save, Rebuild

Update Model from Database.

Then:

table AB is nowhere to be found in the Model

table AB is nowhere to be found under EntityTypes of the DataModel

I can see AB in the Model Store under Tables/Views

I am at a loss how to get this table showing and hooked up.

Please advise