In the Inventory Screen, with secondary weapon equipped and currently set as main weapon (hunter's bow in this exmample), when equipping or unequipping any other inventory item (ring, cloak, etc.), both the Primary weapon and Grimoire 'flash' onto the screen over the character's left hand (the hand holding the bow).

 

Don't have this on my Aloth. Hunting Bow correctly replaces grimoire.

Hello, Danger McTrouble.  I am unable to reproduce this bug with the newest internal build.  Can you please upload a saved game and output log to something like Dropbox and then post a public link here for me to download?  That will enable me to take a closer look at your issue.   Thanks for your support and patience during this issue.