Unable to create new Namespace in Price Editor

[Jonathan Wells]

I am trying to create a new Namespace in the Price Editor in order to 
create a commodity for recording vehicle miles at $0.xx cents per mile.  
The Namespace would be entered as "MILEAGE".

As I understand it, I should be able to type a new Namespace directly 
into the Namespace box in the Price Editor Add Form and it should be 
created when the commodity is saved to the database.

I can type into the Namespace box OK.  However, as soon as I tab out of 
the Namespace box (ie Namespace box loses the focus) , the Namespace 
reverts to the last value it had.  This is always a value that is on the 
drop down list  (CURRENCY, FUND, NASDAQ, NYSE etc).

For instance, the value in the Namespace box is "CURRENCY" when I open 
the Add price dialogue.  I overtype "CURRENCY" with "MILEAGE".  I tab 
out of the Namespace field.  The valu of the Namespace textbox reverts 
to "CURRENCY".

Am I missing a step somewhere ?  I'm using GnuCash 2.6.12 on Windows 7.

Thanks!

Jon