SellXfr changes to negative BuyXfr

I just entered a SellXfr transaction -- something I haven't done 
much, perhaps never. I had just placed the sell order, so I didn't 
have all the details, but wanted it represented in MD for planning. I 
was selling from a bond fund, so I knew what the exact dollar amount 
would be, but not the number of shares.

So I entered a future date, SellXfr, entered the receiving account, 
left the shares blank, and entered the dollar amount. The price per 
share was already present (may change a cent or two, but I can deal 
with fixing that later). And hit Enter.

I was expecting MD to calculate the number of shares based on the 
dollar amount and the share price. After all, MD is usually fairly 
aggressive at adjusting one of the three figures when I alter another 
-- enough so that I had to get used to entering them in the right 
order so that both dollar amount (for the external or cash account) 
and share count (for the investment account) would come out right.

MD left the share count blank, changed the txn type to BuyXfr, and 
negated the dollar amount. This resulted in a very odd-looking txn: 
BuyXfr, no shares, negative dollars.

Is there any reason for this behavior? Or is it just a fall-through 
case? If it's inadvisable for MD to calculate the share count in this 
case, I'm happy getting an error message and being told I have to do 
it. (That's what I ended up doing -- just entered the formula in the 
shares box.) I can't recall whether MD ever rejects a txn entry -- it 
would make sense that MD would try to avoid discarding the 
information, even if it needed correcting. But twisting it like this 
doesn't make sense.

Anyway, that's the long story, I haven't decided whether to bother 
with a formal report.

Edward