Description of problem:
Sorting of task lisk based on Id/Name/Priority/Status/DueOn by clicking at column headers no longer works (it worked previously in DR5)

Version-Release number of selected component (if applicable):
6.0.0.Beta 5

How reproducible:
Always in my environment with Firefox 22 / Fedora 19

Steps to Reproduce:
1. Go to Tasks > Tasks List
2. Add several task using New Task (different priorities/names)
3. Click column headers (Id, Task etc...)

Actual results:
The list is not sorted

Expected results:
Sorting of list based on value in column, on whose header user clicked.
Repetitive clicking should switch between ascending/descending sort order.

Additional info:
Ability to organize the tasks by various criteria is one of the PRD requirements (PET-9)

There seems to be the same issue in "Process Definitions" and "Process Instances" tabs. On the contrary, if you check "Process Instance Details", there is a table of process variables, in which the sorting works as it should.