Okay so I've played some Castle Wars recently and I got 150 tickets.
I' thought by myself which brawling gloves should I take.
I couldn't decide so I took one prayer and two smithing ones.

So my I tried them out, but what happends when you have two of the same brawlers at once? The charges of both gloves reduced.

e.g.
Before I used the superheat it said it has 499 charges left.
When I wear 1 pair of smithing gloves before I used the superheat it said it has 499 charges left.
After the superheat it says 498 charges left. (That's right)

But when I take my other Brawling gloves (smithing) from the bank, and check it's charges, it also says ''Your Brawling gloves (smithing) have 498 left until they crumble to dust.''

This amount should still be 499 since I didn't use it while smithing/smelting.

That's not a bug, 2 gloves give you 1000 charges nonetheless. I'll try to explain how it works:
The server saves a value for brawling gloves (smithing), that's the charges. It starts with 500. Whenever you use your brawling gloves (smithing) that value is decremented until it reaches 0. At 0 a pair of brawling gloves (smithing) degrades to dust. It doesn't matter which pair of the gloves degrades. The server then resets this value because he sees you're using your next pair of brawling gloves and starts its counter at 500.

You have the same mechanic with barrows armour too.