Yeah, beast form's right click action seems to be handled differently than the others. It's also the only one that happens when right-clicking over a shiny.
When right-clicking an ancient turtle, for instance, Naija's sing menu won't come up, energy form won't shoot a spark, nature form won't plant a seed. But beast form, the only form whose shot depletes, will fire a shot. This isn't really an issue if you use keyboard commands, because you can just hit the key you have bound to 'revert' and beast-form won't shoot. But if you're playing with mouse only it can be a huge pain.