Hello. I am not able to print out for example an Page size of 240mm (wide) x 180mm (long) with LibreOffice.
This bug seems to be also in Linux - thanks to testers in #libreoffice IRC.
How to reproduce this bug:
Make an new file in for example Writer. Change page Size to 24cm x 18cm. Then you can already print it. You would see, that it changes the size automaticly from the size that is been set to B5. B5 is longer and breaks the document when printed (missing text on one side and white space on other).
When you configure the custom page size and then go back, the preview still show B5. When you open again the page settings of the printer, some drivers reimplement that what LibreOffice sets by itself: B5. So you set custom, press ok. Open again and its been set back to B5 again.

The used printer is more modern. So i could do this test:
I entered in the printer settings on the printer monitor itself wrong page settings. In this case it tells me what size is been send to the printer and asks me if i want to put in correct paper or print anyway.

I have an simple docx file configured with 24cm x 18cm for testing M$ and LibreOffice with same file. When i open it in Microsoft Word and print it(making no custom print-settings), the printer screen ask me if i would like to print custom page format.
Now i open same file with LibreOffice 4.4.1 .I say print (again not making any custom print-settings). The printer screen ask me if i would like to print B5.
LibreOffice installation is clean with fresh LibreOffice userprofile.

As told, you already can see in the printing preview before sending the page to the printer, that LibreOffice have set the Page to B5. So when testing you dont have to print it out every time.

On Linux other user have tested it and get same problem.

In short: It seems impossible at the moment to send an page with size 24cm x 18cm with LibreOffice to the printer.