K- original issue had to do with Matrix and autosave- see P&T bug report:
https://getsatisfaction.com/pixelandtonic/topics/matrix_and_autosave

Using EE 2.2.1 I get the following error from Matrix when the autosave kicks in. Using Matrix 2.2.2.1.

Severity: Notice
Message: Undefined index: fields
Filename: matrix/ft.matrix.php
Line Number: 1823

...

The first occurrence I see of $this->cache[‘fields’] is in the validate function… I’m betting the autosave isn’t calling validate.

I was betting we didn’t call autosave either- because it meant a missing required field would result in no autosaved data.

However- we are validating autosaved data- _check_for_data_errors.  So I take a look at the ajax response after making a textarea required and not filling it in:

“success”:“Autosaved at 01:22 PM”,“autosave_entry_id”:{"Body":"The following field is required:"},“original_entry_id”:0}

Don’t let the success fool you- db is not being populated.

I suspect the matrix issue occurs because our internal ‘required’ check kicks in before field validation is ever run- but I won’t swear.

Just skipping the _check_for_data_errors() if autosave is true also causes errors in a quick test-

A PHP Error was encountered

Severity: Notice
Message:  A non well formed numeric value encountered
Filename: api/Api_channel_entries.php
Line Number: 140

Not that I’m at all sure that’s how we’d want to handle it anyway.

So- this one needs some thought- what if any validation do we need to run on autosaved data.  I really don’t think any- but obviously this is problematic at present.  Also- we need to keep the Matrix issue in mind- I think that may be better addressed on their end, but like ‘revisions’, we need to be careful of third party fields and how they may have things structured.