There is no useful gaming here. Removing a vote does not benefit you in any significant way, other than: a) making the recommendation feature work better for you, and b) slightly increasing the payout on other posts (generally insignificant).

More specifically, voting is in effect spending the perishable resource known as vote power (which recharges from empty to full in five days). Removing the vote does not give you back the voting power you originally used, so you end up worse off than had you left the vote there (assuming the vote would have earned a reward >0).

Obviously this corresponds to your case (b), which as you say is the less interesting, and perhaps means that people won't remove erroneous votes. Even there, the incentive is to be a bit more careful and not make too many errors (which could mislead others about the state of voting). This is not necessarily a bad thing. The designers of the platform identified the same issues you did with (a) so they did not use it.