Add another button breaks Entity Reference values

If the Field Collection contains Entity References, when the 'Add another item' button is clicked, a new row is added, but all values for the Entity Reference (for all rows) are lost.

The Entity Reference values use a Select list widget. The values to build the Select list use an Entity Reference View, with a contextual filter, to build the list of possible references. The contextual filter in the View uses a default value, and I've tried using a URL argument and an OG context. Once the 'Add another' button is pressed this contextual filter value is lost, so the View returns it's fallback value (ie, the filter value does not validate); if this fallback is hide all values, then the Select list has no values to select, and the entity reference value is stripped from each row. And I've also tried Autocomplete widget, but this fails too.

So where has this contextual filter value gone when the field collection table is rebuilt? Is this a Field Collection (rather than an FCT) issue? I would have thought a URL value would be fairly robust...

The temporary workaround I have at the moment is to set the Views contextual filter fallback value to serve up all values - but this won't be practical once live.

There seem to be a lot of Issues related to how the table is rebuilt once 'Add another' is clicked. I've found the problem, but no idea of a solution. Grateful for any thoughts.