Steps to reproduce:
1) login into cockpit (in the develop profile)
2) go to the (runtime) process definition view of the process "Cornercases Process" (make sure that one of the process instance has variable named "dateVar" and the value of the variable should be a date greater than "2016-02-26T09:24:08")
3) add the following variable filter: dateVar>"2016-02-26T09:24:08"
No process instances are found
The (plugin) backend does not recognize that the given query value "2016-02-26T09:24:08" is a date and handles it as a string value (see https://github.com/camunda/camunda-bpm-webapp/blob/master/src/main/java/org/camunda/bpm/cockpit/rest/dto/AbstractRestQueryParametersDto.java#L100-L105)