Field Blank and Lost After Update

i have a field group, and then i add some new field.
the problem, when i click the Update button, the field on 2nd position (whatever the type of field) go blank.
when i try to edit blank field and click the update button again, nothing changes still blank
and when i delete the field, the other field in 2nd position going blank like the deleted one before.

WordPress 3.8.1 + ACF 4.3.5

i’m sorry for my awfull english 🙂

https://wordpress.org/plugins/advanced-custom-fields/