[GNC] Rate column appeared after Balance

[Colin Law]

Using 3.5 on Ubuntu , on just one of my Bank accounts a Rate column
has appeared to the right of the Balance column.  I can push it off to
the right but it has a habit or re-appearing.  I am not aware of
having done anything to make it happen.  I imagine it is to do with
exchange rates, but I only use GBP and have checked that the account
is still set to that currency.

I have looked through the preferences, looked in the manual and
Googled to no avail.

Any suggestions on why it might have appeared and how to get rid of it?

Colin