Hi!
this bug occurs also in QA_2_9, so we better fix this before 2.9.0-beta1!
Have a look at libraries/display_tbl.lib.php. Are you looking at this now?
Looking at it right now. Seems to be caused that the SQL query statement now emits
"ORDER BY `table` . `colum` DESC"
instead of the former one
"ORDER BY column DESC".
Thus the proper column type can no longer be matched in $sort_expression on line 480.
I'm looking how to manipulate it to easiest fix it.
Regards, Garvin