Steps to Reproduce

http://zkfiddle.org/sample/o29k1p/1-ZK-4367
Drag the center area of the splitter

Current Result

The center area of splitter can't be dragged

Expected Result

The center area of splitter can be dragged

Debug Information

<splitter collapse=""/> can be dragged
<splitter collapse="after"/> can't be dragged (there is a button)

Workaround