There are a few masteries and specializations that set your maximum companions to 1, no matter whatever other passives you have. The mechanic is working fine, no problems there, but the character sheet still shows the standard number you would have without those passives. I’d prefer it to reflect the actual maximum companion amount.
Specific ones I know about are Natural Duality (Druid tier 8) and Artor’s Loyalty (Beastmaster tier 2).