Table frame partly disappears for cells with morerows=1

I'm trying to generate a table where each cell has full borders. This works OK until
I try generate a header cell spanning two rows with <entry morerows="1">, in which case
no border seems to be generated at the bottom of the cell. The cell borders are being
defined by setting table.frame.border.thickness and table.cell.border.thickness each
to 2px in the stylesheet customization, and default.table.frame to "all". Liberal
use of rowsep="1" in the table <entry> elements seems to make no difference. Am I
missing something here or is there possibly a bug in the stylesheets?

Interestingly a body cell with morerows=1 does generate the bottom border, this
only seems to happen for head cells.

This is using XSL-NS 1.78.1 and generating output index.xhtml via

xsltproc --noout --nonet --xinclude test.xsl test.xml

Minimal case attached including rendered results.

    Thanks,
    Jon