Quote from The Nick:
Just remembered another! All you need is the charge beam and a good distance and have an open door. Have Samus start running but without holding her cannon. Go through the door and as the screen is switching to the next room, hold B to start charging. When Samus continues in the next room, she will still be running without holding her cannon. However, the animation of the charging energy will be following her gun arm as she runs.
imo, that's no glitch, and a rare example of the detail that is usually missing from fusion.