[Libreoffice] Bug 36874 page size incorrect when creating label document - help asked

I am trying to locate the source where the page size is determined when creating a new label 
document with the wizard.
Although the dimensions in the label-definitions for A4 label sheets are correct, LibO creates a 
document with custom page format and not A4.

I can't find where the document is created. Can anybody give me a hint? My goal is to see if it is 
an easy hack and in that case to provide a patch.

Also, there seems to be a lot of duplicates for this bug. I have summarised them in my comment in 
bug 36874. Can anybody who knows how mark them as dumpicates?

Thank you for your attention.


Winfried