This bug was intruduced by the fix for bug#17212 (in 4.1). It is not 
ok to call test_if_skip_sort_order since this function will 
alter the execution plan. By contract it is not ok to call 
test_if_skip_sort_order in this context.

This bug appears only in the case when the optimizer has chosen 
an index for accessing a particular table but finds a covering 
index that enables it to skip ORDER BY. This happens in 
test_if_skip_sort_order.