I hadn't been paying attention, obviously, because this whole topic passed me by. Apparently, players investing in corporations who have more than B$ 1Q invested lose out on interest payments. Whoopsie! Obviously, the quick fix is to withdraw funds so that your invested balance is below 1Q, but what to do with the rest?
A solution suggested to me by another player was to create your own new corp, basically a sole proprietorship, with only you as the member. Corporation interest rates depend on the value of your shares holdings, but with the new math, it isn't hard to amass sufficient holdings (I have no idea what the cutoff here really is...) to earn the max rate of 0.5%. So, invest some sum less than 1Q in your corp, then donate any additional funds to the corp that you wish, and make sure that this is set as your primary corp.
You will then earn interest on the invested amount, and the corp will earn interest on the donated funds, which are entirely under your control. Also, be sure not to reinvest your earnings, or your invested amount will increase to over 1Q, and you're screwed again.