Here is a short video of the crash.
https://www.dropbox.com/s/w28t954g5cpjs01/Minecraft%201.7.10%20160128_072903.mp4?dl=0
Edit: After looking at the logs i realized it had something to do with the mobility mod, after removing it the crossing bars work fine.
Yeah, but still, it's not supposed to do that.
But since WMobility is still in an early stage this isn't that big of an issue, I'm putting it on my list though, thanks for the report.