> Does the problem occur when you compile with no optimizations?

I never use any options to compile.  What shall I use?

>>I could send you the Elisp code I use to trigger this.  You'd have
>>to play around with it a bit, though.
>
>
> Is this the m&d-drag-line-up function that KFS already posted?  I've
> been trying it out on various buffers, and have been unable to
> reproduce it---is there a specific buffer you act on to produce the
> error?

There's also a m&d-drag-line-down function and a pre-command hook.
Initially written while I worked with Emacs 20 (and transpose-regions
was somehow broken IIRC) and awfully patched a couple of times
afterwards.  I attach it.  To reproduce bind the drag-line functions to
a key and use the auto-repeat functionality of the keyboard (I use a
hyper key and the arrow keys for this purpose).