When i am viewing active enchantments on a target that had a bounty, the option to cancel the voodoo is there, however it only shows up when:
That voodoo isnt at the top of the list of active voodoo
And
When the voodoo above the bounty casts are not bounty casts.
When i click the cancel option for hostile waters (the bounty voodoo) it asks if i want to cancel drums of war which is on another fleet of mine instead of cancelling the hostile waters.
Try this out. Have someone set a random bounty on an inactive, then cast a hands of gold, then the bounty enchantment and check your active curses. The bounty enchantment has a cancel option.