accounting absent from cash accounts on stock buys

[cognitive.libertarian+ml at gmail.com]

After entering a stock purchase, the cash account that the purchase
draws from is not properly reflecting a decrease.  A row appears in
the cash account, but both the "Increase" and "Decrease" columns are
automatically blank.

When trying to correct this manually by entering the cost basis in the
"decrease" cell, the error: 

  "You need to expand the transaction in order to modify its exchange
   rates"

What can be done to make the cash register properly reflect the cash
balance after a stock transaction?

Could this issue by caused by having the stock account as a subaccount
of the cash account?