I'm not a maintainer of the tablesorter plugin, but I do know (as you've found out) that the sort cache fails when applied to a different table.

Work-around:

• Don't clone including data and events, you're creating a new table essentially. So call .tablesorter() on it if you want it to be sortable.

$('table.sortable').first().clone().appendTo( mw.util.$content ).sortable()

(In reply to Krinkle from comment #1)

Work-around:

• Don't clone including data and events, you're creating a new table

essentially. So call .tablesorter() on it if you want it to be sortable.

$('table.sortable').first().clone().appendTo( mw.util.$content ).sortable()

Now with mw.hook('wikipage.content') it is possible to do

$clone = $('table.sortable').clone();
mw.hook('wikipage.content').fire($clone);
$clone.appendTo(mw.util.$content);

This seems a reasonable approach to me, and I no longer consider it as just a work-around, but as an actual solution. So let's just close this as WONTFIX.