In the renderTableHeader() method of the Column class, the actionLink is retrieved from getTable().getControlLink().
This method sends back the ActionLink used for paging, but...
The problem is that the title of this ActionLinks is already set to getMessage("table-last-title") in the renderPagingControls() method of the Table class if the banner position is TOP or BOTH, and it is not set again in the renderTableHeader() method.
Proposed solution : at least set the title of the retrieved ActionLink to somehting meaningful in the renderTableHeader() method, like controlLink.setAttribute("title", getMessage("table-sort-links")), where the entry would resolve to "Sort by" in the click-control.properties file ("Trié par" in French).
Easy to fix for the 1.4 release, I think.