Bug: Infernal Instability does not give you any hint that its buff (the movement slow resistance) is active on you after you hit someone.
Replicate: Activate the ability, hit someone and notice no tooltip.
Bug: Grapple is bugged in that if you use it on max range, it doesn't continue moving 725 distance. If you only got rank 1 and shoot it at max distance, the gauntlet will continue up to a distance of 725 in total, if you got a higher rank and click on maximum distance, it will not fly further.
Replicate: Get rank 1, click on ground right infront of you, notice that it travels further. Click further away and notice it does not travel 725 distance further. This holds true for all ranks.
Bug: Cripple is kinda strange as well... I tried giving a lvl 25 Gauntlet 6 warpcleft just to see what would happen if he had insane attack speed, here is what I found; he never got more than 1-2 charges as he kept pounding on poor Hammerstorm (with 6 behemoth hearts), however Hammerstorm initially got up to about 60 charges (from first attack), then dropped down to 25-26 charges no matter how long I kept pounding on him. He could still attack and move, so not just a tooltip error. What I'm wondering is, why does Hammerstorm have 25-26 charges when Gauntlet never gets more than 1-2 charges? And if its meant to increase the more gauntlet pounds on someone, why does it stop at 25-26?
Bug: The ultimate does not purge all buffs, I tested it with Hammerstorm (hellbourne side, i was legion side), I used both his ulti and galvanize then used Gauntlets ulti on him, Hammerstorm still had both his spells active. As far as I could read, there are other buffs he can't purge. Sometimes it doesn't damage the enemy, I couldn't recreate this bug, but I clicked right next to my testdummy Hammerstorm and the gauntlet flew right past him without damaging him.
Replicate: Put in Hammerstorm and active his abilities, then use ulti on him or right behind him, notice he will still have all his buffs after being hit.
Is the buff from Infernal Instability supposed to be active on you after you hit something? From what I can tell the buff is the advantage the skill gives you before you get the aoe splash when you hit something at which point the buff is removed. My theory is the idea is that you can activate it to get the buff and rambo charge in to initiate or charge in quickly before dragging an enemy away towards your team with grapple. I'm not sure about the Grapple bug. I'm not sure why Cripple always stays at around 25-26 charges when you keep hitting someone, but as for the charges, you are mistaken to think they are supposed to stack. Read the tooltip; it says that when you hit someone and the charges are applied, any previous stack is removed. This is to prevent you being a super fast attacker and disabling someone with a 100% cripple. As for the ultimate, I haven't really checked, so I'll give your bug the benefit of the doubt.
Instability grants movement speed slow resistance to you for 4 seconds after using the skill.
Grapple should be intended.
Cripple staying at 25-26 should be intended as well. Do some math and you should find that the highest you can keep it is about 26-27. It is to prevent 100% slow.