Question Non-OP'd players can't spawn entities

I'm currently using Bukkit on my server and am running several mods + plugins.
I've come across a problem where the mod "Animal Bikes" will only spawn the entities if you're an OP.

I've taken off all the mods (except Animal Bikes) and have taken off all the Plugins and still experienced the issue.
I've also tested this is on a client-based server to test the mod and did not experience the issue, so I'm assuming its Bukkit.

server.properties
bukkit.yml
permissions.yml is empty

Is there anywhere I should be looking or are any of my settings preventing the spawning of entities of non-OP'd players?

PS: I had Essentials and bPermissions, but I'm not sure if any of that is relevant since I removed all of the plugins and mods at one point to test the issue and it persisted.

Thank you!