Can't set Work Item handlers from workbench

I'm trying install two versions of jbpm - 7.5.0 and 7.7.0.

See attachments. Whem i'm using jbpm 7.5 - I can set WorkItemHandler in editor, but in version 7.7 Work Item Handlers block lost and i need add it in text editor.

Sorry, I'm noob in JBPM and don't understand what is it, but wihout that handler my process didn't work