Deadlock on cursor open??

Why does opening a cursor sometimes return a deadlock error? Does the server (OnLine) assume that I am going to fetch the first row at least and attempt to place a shared lock on it in advance? (The program is running in cursor stability isolation.) If the above guess is true what is the justification for this behaviour? Sureley the fetch is what should place the lock or does the server place the locks itself on the data it has buffered up? Mike.