Pretty easy to reproduce and has some non-damaging consequences (in my experience).

Setup a hook near your bed with any of your grappling hooks, go to bed. While in bed you'll move around due to the grappling hook.

Mod information:
MCP: 9.05
FML: 8.0.99.99
Minecraft Forge: 11.14.3.1450
Player API: 1.4
Smart Core: 1.2.1
grapplemod: 1.0
Smart Moving: 16.2
Smart Render: 2.1