Flow widgets overwriting one another?

[tropcicstefan]

We have headless orchard for one news room and since we upgraded from rc2 to 1.4 suddenly widgets inside flow part occasionally started to overwrite one another.
For instance widget with datetimepickerField and taxonomyField being overwritten by a widget with htmlBodyPart.
In json in db widget preserves it's ContentItemId but it changes it's ContentType and 'body parts'.

Any idea how to debug that because it only occurs in production occasionally?
It happens on save (publish or draft) so maybe payload is sent with wrong index? I was trying to find something in flowpartDisplayDriver but nothing on first look.
Is there any way to log POST payload to see f indices of widget get mixed up?