cleanupFieldFormState causes multivalue field rows to disappear

The function EntityInlineEntityFormController::cleanupFieldFormState() causes multivalue rows to disappear in modules that make use of items_count. Two examples are the date and field_collection modules. When cleanupFieldFormState is executed after save, it sets items_count in the field's state to zero. This results in missing items if an entity's row is reopened for additional editing after an initial save.

I think this is the easiest way to reproduce the bug:

• Install the date module.
• Create a node type called "Date."
• Add a date field, and set the number of values to unlimited.
• Create another node type called "Date Collection."
• Add an entity reference field:
  • Use the inline entity widget.
  • Reference the "Date" content type you made earlier.
  • Set number of values to unlimited.
• Create a new "Date Collection."
• Using ief, add a date node. Enter 2 dates and save.
• Reopen the row you just created, enter a 3rd date, and save.
• Reopen the row again. Instead of having 3 rows, you only have 1.
• Press "Add another item" a couple times and watch the 2 missing rows get resurrected.

You can also get strange results when hitting Cancel. Try this:

• Add a new row with just one date. Save it
• Reopen the row, and add 2 new dates, but hit Cancel this time.
• Reopen the row, and see 2 empty ghost-dates.

Similar problems occur with field_collections configured with an unlimited number of values.