DOCBOOK-APPS: Page number sorting in automatic index

When I render a document using XSL 1.58.1, the page numbers listed after the
index term are in descending instead of ascending order (i.e 120, 98, 13
instead of 13, 98, 120). Is this a known bug ? Is there a simple fix I can
make to have it sorted properly.
I tried to dig into the code but could not find anything that actually
worked....

Thanks in advance,
St廧hane.