How to get rid of "Could not determine the account currency. Using the default currency provided by your system."

[Paul Neuwirth]

Hello,
I always get "Could not determine the account currency. Using the
default currency provided by your system." when opening an account since
upgrade to 2.6.19.
according to SQL 
SELECT * FROM gnucash.accounts a left join gnucash.commodities c on
c.guid = a.commodity_guid;
all accounts have a currency set.

Book Option "Use Trading Accounts" is off
Preferences Accounts, Default Currency is set (choose: EUR)

what am I missing?

Any help appreciated.

Happy new year,

Paul