Sort of columns doesn't seem to work correctly in Process Instance List.
If you click on "Start Date" you get the error (from Firebug panel):

Thu Sep 12 14:23:09 GMT+200 2013 com.google.gwt.logging.client.LogConfiguration
SEVERE: Exception caught: For input string: "12/Sep/13 08:56:05"
com.google.gwt.event.shared.UmbrellaException: Exception caught: For input string: "12/Sep/13 08:56:05"
at Unknown.d0(StackTraceCreator.java:174)
at Unknown.Qf(StackTraceCreator.java:501)
at Unknown.G$(RuntimeException.java:33)
at Unknown.seb(UmbrellaException.java:71)
at Unknown.veb(UmbrellaException.java:26)
at Unknown.Pdb(UmbrellaException.java:90)
at Unknown.gxd(ColumnSortEvent.java:160)
at Unknown.mn(AbstractCellTable.java:1914)
at Unknown.mm(AbstractHasData.java:739)
at Unknown.WAd(DOM.java:1307)
at Unknown.anonymous(DOMImplStandard.java:171)
at Unknown.y_(Impl.java:189)
at Unknown.B_(Impl.java:242)
at Unknown.anonymous(Impl.java:70)
Caused by: java.lang.NumberFormatException: For input string: "12/Sep/13 08:56:05"
at Unknown.d0(StackTraceCreator.java:174)
at Unknown.Pf(StackTraceCreator.java:501)
at Unknown.Tf(Exception.java:29)
at Unknown.F$(RuntimeException.java:29)
at Unknown.$3d(IllegalArgumentException.java:29)
at Unknown.j5d(NumberFormatException.java:33)
at Unknown.u2d(Number.java:286)
at Unknown.pfk(ProcessInstanceListViewImpl.java:366)
at Unknown.rfk(ProcessInstanceListViewImpl.java:364)
at Unknown.oxd(ColumnSortEvent.java:122)
at Unknown.Cce(Arrays.java:1250)
at Unknown.Fce(Arrays.java:1318)
at Unknown.Ece(Arrays.java:1296)
at Unknown.Yce(Collections.java:956)
at Unknown.jxd(ColumnSortEvent.java:120)
at Unknown.dxd(ColumnSortEvent.java:225)
at Unknown.fxd(ColumnSortEvent.java:224)
at Unknown.Zdb(GwtEvent.java:76)
at Unknown.Pdb(HandlerManager.java:127)
at Unknown.gxd(ColumnSortEvent.java:160)
at Unknown.mn(AbstractCellTable.java:1914)
at Unknown.mm(AbstractHasData.java:739)
at Unknown.WAd(DOM.java:1307)
at Unknown.anonymous(DOMImplStandard.java:171)
at Unknown.y_(Impl.java:189)
at Unknown.B_(Impl.java:242)
at Unknown.anonymous(Impl.java:70)

Then if you go to next page, clicking on the >>| button, the sort sseems to happen but probably it's alphabetical (that doesn't fit well to dates).