In this video you will see the glitch/bug in question. It seems like more than just a cool down because it sometimes happens after re-spawn and is not related to previous sprinting. It happens very often and is the only troublesome user experience in Destiny, in my opinion. Bungie can you please comment on this, Bug or Cool down?
An example from a re-spawn can be seen in this video:
https://youtu.be/1iFJyTiIS6U
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Might be because in real life, damage to you body makes you slow down, not able to run until it heals. It makes sense to me, at least.