Bug in Smallcase

Hi, when creating a small case, I have the option of specifying percentage or number of shares. I create a small case specifying the number of shares of each stock and save the small case as a draft. But If I go back and modify the smallcase, say I add a new stock to small case, it changes the values I had input earlier. It changes the number of stocks to a percentage based on the price of each share.
Could you please guide me as to how to circumvent this problem or is this a bug in the system?