Document entity translation for nested field collections

This is a follow-up to #1344672: Field Collection: Field translation (entity_translation) support., which I am documenting as best as I can, but there is a workaround (explained below), so I am unlikely to be able to follow up further on this too much.

If a field collection field within a field collection (i.e. a nested field collection) is translatable with entity translation, translation does not work correctly.

For example, with the following fields set up:

node (translatable with ET) -> translatable field collection field -> translatable field collection field -> translatable field(s)
Both field collections at each level also contain other translatable fields of other types.
Nodes, but not field collections, are set as translatable in the ET settings at /admin/config/regional/entity_translation (maybe that's the problem, though in that case, it should be clear somewhere in the UI that that is an impossible combination of settings?? I haven't checked that.)

...First create the node, in a language (i.e. not Language neutral), entering values at all levels and this saves fine. But then go back in and edit the node - the values are not there. If you then re-add the values and save the node then go back to edit it it retains the data this time. Potentially that's because the first time around, values are being saved as language neutral, but then on editing the node, the values are trying to be retrieved from the node language instead?

I imagine there are other combinations of un/translatable fields at different levels, for example, I couldn't get it to work with only the 'deepest' level of field being translatable either.

WORKAROUND: The only reliable way I could set up my fields was to have the node and just the top-level field collection field as translatable.

Edit: Changed from bug to task to improve the documentation since the module is working as designed.