I've entered a vlookup formula and when I copy it to another cell, sometimes
it copies the formula correctly into the other cells and comes up with the
correct (and different) results but sometimes when I try to copy it, it just
copies the previous result--and ignores the vlookup formula altogether.

If i go to the cell and place the cursor in the "fx" field as if i was going
to correct the formula, but not make any changes, and press "enter" the
result gets corrected. This is a problem if i have a whole range of cells as
i don't want to go into each cell to fix it.