I can not change the paper size 10x15cm (4x6") in the "Page Setup" dialog.

If you select "Custom", then specify the size manually just does not possible (the required elements of the window are inactive).

In the version for Windows this option possible select after change printer, but in the Linux version, the printer selection dialog appears after clicking on the button "Print", and does not affect positively on the printing process (fragment sheet of A4 printed on paper size 10x15cm).
Please tell me it is a bug XnView MP or I do something wrong?
Thank you.