Cannot use secondary weapon skill on Rhoa mount

I have set my secondary weapon to use my equip primary weapon, this is to use Stormcaller arrow. Of course to benefit from secondary weapon passive points to increase the shock magnitudes.
However, if i do not cast stormcaller arrow before mounting the rhoa, then i cannot use it until i dismount/roll then remount.

Has anyone else had this issue and managed to resolve it or is there an issue here?
Thanks.

I have the exact same issue where my main bow in slot 1 is locked to weapon slot 2 and only attacks that use weapon slot 2 stop working when mounted on the Rhoa. I have not found a fix but I am posting in hopes of finding a resolution.