Multi Value Custom Field importer broken on 4.7

The multivalue Custom Field importer is broken as you cannot select any custom fields for the selected multivalue Custom Group.

It would appear it was this commit that broke it https://github.com/civicrm/civicrm-core/commit/81c3812a8fa41b3644c07b27baabd90630108023

The situation appears that the value of multipleCustomData which equates to the id of the custom group that is selected is not being stored so when mapping does an API call to get the fields for the selected custom group it fails as it has no id for the custom group

to reproduce

1. create multivlue custom group that extends individual and a field
2. go to civicrm/import/custom and select group from 1
3. in mapping find you only have option of contact_id and not field created in 1.