Foreign currency account not balancing

[Floyd Hagen]

I have an account in a Japanese bank, and I've been moving funds from it
to my bank here in the States.  When I transfer funds from the Japanese
account, which is in yen, I expected gnucash to do the math to convert
and balance the Japanese account out. However the balance in the JPY
account remains the same even though money is added to the USD account.
Did I miss something? 

Thanks