Does conditionality work for table cell borders?

Hi list,
When a table is continued across page breaks, I would expect the before-border of the table cells to be suppressed on all pages after the first (unless I explicitly set the conditionality to "retain"); however, in my example document, the borders are visible on the second page.
You can find my example FO document at https://www.dropbox.com/s/w679cjb9gampdq6/table-borders.fo?dl=0 and the result PDF document at https://www.dropbox.com/s/bpc5avwsrzb8k6j/table-borders.pdf?dl=0
I thought this might maybe only work for the table-row elements, so I tried it there, but the result is the same. Besides, as you can see in my example, I need the border for the *cells*, not the whole row (because I want a gap in the middle).
I use FOP 2.5.

What do I miss?

Thanks,
Christian

PS: I found http://apache-fop.1065347.n5.nabble.com/Omitting-Bottom-table-border-on-page-break-td37527.html, but this only points me at the conditionality, which should already implicitly be "discard" in my case.