Inline editor is not opened for custom object if class sheet is in 2.0 syntax

I followed to wizards and created class sheet for custom class is in 2.0 syntax.
Though I found that object doesn't want to open inline form on simple editing and needed to open inline form explicitly.
After investigation I found that if class sheet and object wiki content is in 1.0 syntax, it started to work correctly (ie. opened in inline form as expected).