I did not catch this bug, a guildie did (Solaar) but I felt like the community (and hopefully Devs) should be made aware of it.
You will notice that every time you change specs you will toggle from fast mode to sluggish mode.
The Speed-o-Meter addon clocks me at 6.5 in fast mode and 5.4 in slow mode (I don't know the units). This is a pretty large (20%) difference in run speed and could leave you scratching your head as to why everyone else could run out of the fire and you couldn't.
To avoid being a slowbie, get the Speed-o-Meter and change specs until you know what your top speed is (will vary based on buffs, PA, conquest power, etc). Then whenever you change specs you will have to change twice (once to toggle slow mode on and once to toggle fast mode on).
We have seen this bug on every class, not sure if it affects different specs differently (ie those with runspeed bonuses).