Derivative Format not Created

Under a special condition Gallerix does not create a derivative format after the upload of an image: If the size of the uploaded picture is identical with the size of derivative format, this derivative is not created.
Example: On a website gallerix has the two derivative formats "Thumbnaix" (58x40 px) and "Frame" (582 x 350 px). When I upload an picture that is larger (allowed up to 1200 x 1200) the "Frame" is created and stored in the corresponding gallerix folder. If the size of the picture is exactly 582x350 px the "Frame" is not created - which is okay, but in this case the original picture should be copied to the "Frame" folder. The missing "Frame" derivate causes gallerix not to show the large picture. The Thumbnail is shown in the gallery and if someone clicks on it, gallerix tries to load the "Frame" without success.