Update hibernate-type process variables via form template

In the Freemarker template attached to my task node, if I have a form field that references a process variable of a simple type, String e.g.,

[input type="text" name="stringProcVar" value="${stringProcVar}"]

the process variable stringProcVar is updated on form submit. However, if I have a form field that references 'objvar', a process variable that is of type 'hibernate entity with a string id':

[input type="text" name="objvar.property" value="${objvar.property}"]

the properties of 'objvar' are displayed correctly in the form. However, updates to the value (input field on form post) do not update objvar's properties. Instead, a new process variable is created:

(server.log)
DEBUG [org.jbpm.pvm.internal.model.ScopeInstanceImpl] (http-127.0.0.1-8080-5) create variable 'objvar.property' in 'execution[ESP-9]' with value 'abc123'

It would be nice if the form processor would update the 'property' on the existing variable 'objvar' and then update (persist) objvar.