From the Wikipedia page cited:

  As with quicksort, quickselect is generally implemented as 
  an in-place algorithm, and beyond selecting the kth 
  element, it also partially sorts the data.

When the above is applicable, those quickselect implementations would violate the original assertion of:

  Only the median (or pair around the median) needs to be 
  sorted, the other numbers can be unsorted

When the collection involved is immutable.