Not a bug.
Stone Gauntlets provide a benefit (increased armour) and a penalty (the slowed movement and attack speed). The intention is that you’re expected to utilise other items or abilities to remove the penalty but keep the benefit. For example…
- Equip or Cube the Ice Climber boots
- Use an Invigorating Gem at Rank 25 or higher
- Maintain 100% up-time on your class’s uber-ability, e.g. Wrath of the Berserker on a Barbarian, Akarat’s Champion on a Crusader, and so on.