losing keyframes after copying

We're having two timeline problems:

1) After copying a series of keyframes from one layer to
another using alt + drag, we'll come back to that series later and
find that the keyframes have changed order

2) The top two layers of a scene will become extended by 1
frame, with all other layers unchanged. In other words, the top two
layers will become 91 frames instead of 90, with all other layers
stayng at 90 frames, even though we've done no work in those 2
layers.

Anyone had similar problems, or know a solution. Thanks very
much.