Weird OFX file import problem

[msalists at gmx.net]

   Hello,
   I have a problem with importing OFX files.
   The very first import into a newly created account works, but trying to
   import additional OFX files for the same account comes up with no
   transactions to be imported.
   Using an entirely new GnuCash file (sqlite storage), I narrowed it down
   to the following:
   I have two OFX files from the same bank (Targobank Germany, ex
   Citibank).
   File A.ofx is from June, file B.ofx is from October.
   I have only the basic account structure setup, no bank account set up
   yet.
   I import A.OFX and chose to create a new bank account "Targo" in the
   process.
   The transaction import dialog comes up with the list of all
   transactions and I import them without changing anything.
   Then I proceed to import B.ofx. The transaction import dialog comes up
   empty with no transactions.
   In order to show that file B.ofx in itself has no problems, I remove
   the account "Targo" and chose to delete all transactions in it.
   Then I import B.ofx, and chose to create a new account "Targo2" the
   process.
   This time, the transaction import dialog comes up with all the
   transactions in B.ofx.
   I import them without changing anything.
   Then I try importing A.ofx, which fimported fine earlier. This time,
   the transaction import dialog comes up empty.
   The transaction that had been listed earlier when importing into a new
   account "Targo" do no longer show up.
   What could be the problem here?
   Thank you in advance for any help...