MD is based on accounting principles, so all "pennies" must add up. I don't think that MD works on a half penny basis (except in securities), so if you spent 30.19, you have to allocate 30.19, not 15.10 twice and expect it to stay 30.19
Hope that helps (even if the answer isn't what you wanted to hear).
So the answer is even if the split is "even" - it really isn't the total is 30.19 and you allocate 15.10 to one category, and 15.09 to the other.
Concur with this suggestion. MD seems to focus on re-calculating the total as the sum of the splits -- but when a total has already been entered or downloaded, keep it un-changed and if necessary leave an uncategorized split row for us to sort out.