Pretty much what the title says. Since the update, I can start my mounts sprinting just fine, but they resume running at a normal pace just a second later, regardless of whether or not I hold down my sprint modifier (shift, in this case). It's not an issue with my keyboard; I can hold it down AND TYPE LIKE THIS with no problem.
Sometimes, after my mount has resumed slow-running with my sprint held in place, I'll release it, and several seconds later my mount's stamina bar will suddenly drop close to zero, like it had actually been draining stamina that whole time--again, with no effect to movement after the initial keypress. And their sprint bar will usually reflect this, with just a small dip that quickly refills even while I'm holding the button, until it suddenly drops to nothing.