the situation:

column A with id's, followed by column B with a lookup function, to find a
value, belonging to the id from a list in another worksheet, but in the same file.

id's are unsorted in the first place

example: in cell A1 is an id, in cell B1 is a lookup function, the lookup
searches in a list in another sheet for the value from cell A1.
the same for cell A2: the lookup function in B2 searches for the value of A2 in
that list
etc.

the problem:

When both columns are selected and sorted by the first column (holding the id),
the search function should follow the new location of the cells in the first
column, but it doesn't.

example: if row 1 moves to row 7 after the sort, the lookup in cell B7 should
look for the value in A7, because the content of cell A1 has moved to A7, but
the function still points to cell A1.

It used to work fine in 3.0.1, in 3.1.0 it's broken.

I prepared a very simple file demonstrating what goes wrong. I hope I find a way
to attach it...