fixes issue #15

Hello!

Thanks for this great little library; it does what I need simply and with a minimum of overhead.

I *think* that this properly fixes #15. I created a unit test that confirms that navigating from /1/detail to /2/detail properly updates the sub-segment content. I basically altered the logic to always include updates for sub-segments once a higher-level update has been created. However, I barely know this code, so if you think there's a better fix, please let me know!