If I try to enter a domain like this 

[("parent_id","=",partner_id)] 

 using the Studio editor, it tells me that is "not properly formed", but if I enter it directly in the form XML, it works perfectly.

The bug also triggers if you try to modify a domain in some predefined fields, for example if you try to edit the domain of the "Invoice Address" field of the Sales form, Studo gives the same error.