It is not possible to map the value of a form variable to a process variable.
Steps to reproduce
1. In activiti-app import the attached app "FormVarToProcessVarFail.zip" in App Designer and publish it
a) App comes with a process start event -> user task -> user task -> end event
b) Process defines an integer process variable "targetVariable"
c) First user task is using a non embedded form that defines an integer form variable "formVariable" with default value 99
d) For this form a mapping is configured from "formVariable" to "targetVariable"
2. From the published app, start a new process "MapFormVariableToProcessVariable"
3. In the first user task fill in some text for the "SomeTextField" field and complete the task
4. Switch to activiti-admin and inspect the running process instance and it´s variables
The instance has a process variable named "targetVariable", but it is from type "null" and has an empty value. The value entered for the form field got correctly set as process variable "sometextfield". The mapping from the form variable to the process variable did not work.
There should be a process variable "targetVariable" from type "Integer" with value "99"
Reproduced in latest APS 1.7 release