It seems that it's possible to increase the amount of your Animal Empathy henchmen by getting off a horse when the number of your henchmen is maxed out.
Steps to reproduce the Bug:
1. Mount a horse.
2. Get two animal henchmen.
3. Dismount a horse.
4. Attempt to get another animal henchman.
Expected Result:
Inability to get more than two AE henchmen.
Actual Result:
A horde of various animals is following me into battle.
Screenshots


Additional Information/Notes
It could very well be that there are other ways of increasing that limit other than horse dismounting.
It probably only affects Ranger characters.