To show bug:
Create a 3 slide new presentation
Select slide 1 and 3 in normal view
do file > export as pdf with 'selection' checked
PDF created with slides 1 & 3
PDF created with all three slides.
Presumably this is a regression from OOo 3.2.1, but I haven't tested that.
Note that from the slide sorter, attempting PDF export with 'selection' checked gives an error message (file cannot be saved).
In both normal and slide sorted view, export as PDF with 'pages' selected and 1 3 in the dialogue box correctly creates PDFs with only slides 1 & 3.
This is an user error because of incomplete instruction in UI and / or Help. "Selection" does not mean "selected slides" (for that you have selection "Slides" under "Range and Copies" in print dialog or "Pages" under "Range" in "Export to PDF" dialog), but "selected area on slide"
I doubt that that works for you when printing ...
Please feel free to file Enhancement bug reports for more unambiguous Help and UI!