Unchanged, updated and saved content all equals for field collection in "Before saving" and "After updating existing" content

Maybe related issues are #1098104: Data comparison of updated and unchanged entity fails if data to compare or data value is empty and #625288: Unchanged CCK (FileField) field values always being seen by rules as changed..

I need a rule that manages values stored in a field collection of two fields (a node reference and a text value) when the user updates the content: there's a calculus involving data's changes, so I have to compare old and new values.
Using event "Before saving" and taking variables "$node" and "$node_unchanged" should be enough, but they give only the changed (new) value. Trying also another rule with event "After updating existing content" leads to the same result.

Moreover I need to manage them in a custom PHP code because I invoke a custom function with something like (in custom PHP code):
if (function_exists('customfunction')) customfunction($node, $node_unchanged);

that contains the following code (it's in a custom module):

...
$wrapper = entity_metadata_wrapper('node', $node);
$field_collection = $wrapper->field_collection; $iterator = $field_collection->getIterator();
while ($iterator ->valid()) {
  $nodereference_nid = ($iteratore->current()->value()->field_nodereference['und'][0]['nid']);
  $textvalue_value = ($iter->current()->value()->field_textvalue['und'][0]['value']);
  $iterator->next();
};
...

and a similar action for node_unchanged: $textvalue_values (for $node and $node_unchanged) should be different (changed in form before saving), but old value is lost somewhere.