it dose not when it is uploaded
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It should only do that in the edit mode. (this makes it easier to rearrange sprites).
try presentation mode. (the tv screen in the top right corner)
if you can still drag it, find the picture of the sprite along with its name and details on the top row. click the lock on the right of the box and make sure it is locked, not unlocked.
if it still doesn't work, make sure your sprite doesn't have a script that tells it to do that
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