I did just do a quick check using Hideous Laughter on an ally, and didn't notice any differences in the current functioning of Prone.
Melee attacks still gain advantage, due to the prone condition, while ranged attacks still garner disadvantage (when at long range, and then becoming a flat roll if taken from melee, due to different advantage/disadvantages cancelling out)
There should be no circumstance where you get disadvantage while attacking a prone creature in melee range - at very worst, it becomes a flat roll, because the one instance of advantage you get from making an attack roll on the target that is prone and within melee range of you cancels out any and all disadvantages coming from any other source. This appears to be working correctly.
(Thought I'll note that the Hideous Laughter status description still implies that failing to save out at the end of your turn, or upon taking damage, results in the victim taking damage... which is completely false in game, and also a complete departure from the original spell... And also, Prone still applies Unconscious, which is, still, completely ridiculous.)
Edit: Meant to say, if you are seeing that, could you double check it and let me know what your situation and set up was when it was happening (the source of the prone condition, the victim, the attack being used that was getting disadvantage, etc.)? If there is a bug occurring somewhere within this status condition mess, I'd still like to replicate it and do a report. "Every little bit", after all.
Last edited by Niara; 05/12/20 12:59 PM.