This has been suggested a couple of times from different sources and would allow better input processing for things like to notify other parts of input events that Nifty did not handle itself.
3126996: Seperate Input-Processing from Rendering Nifty
Attention: You'll need to call update() AND render() now. Just calling render() is not enough. InputSystem processing is now called in update() and separated from rendering.
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
details in here: http://jmonkeyengine.org/groups/gui/forum/topic/nifty-capturing-click/
@public
3126996: Seperate Input-Processing from Rendering Nifty
Attention: You'll need to call update() AND render() now. Just calling render() is not enough. InputSystem processing is now called in update() and separated from rendering.