You can add hundret storages to a bus if you like, there is no limit.
It is possible, that a storage can be loaded and unloaded simultaneously even though it does not make sense in most cases.
You should provide more information about your model to make it easier to give more concrete help.
I guess the storage has an efficiency below 1. That means that the model tries to get rid of some unneeded energy. Do you have another option to throw away excess electricity? If this is the case you could add minimal costs to the storage (0,000001 ct), so that the other option is slightly better. Or you can add negative costs to the other option (-0,000001 ct).
Your result is a consequence of your model design. The solver does not think it is just heading to the best solution. If you have two options that are mathematically the same, different solver may even use different options. It may happen by chance because the solver does not know anything about storages.