Throwing an exception as a result of a normal situation is extremely bad in .net

At the end of the FastCharStream.Refill() method, it says:

int charsRead = input.Read(buffer, newPosition, buffer.Length - newPosition);
if (charsRead <= 0)
throw new System.IO.IOException("read past eof");
else
bufferLength += charsRead;

When I run Lucene in the debugger, this causes an exception to be thrown all the time.
To me it looks like it is thrown as a result of a normal situation, not because of some critical error.

Is this correct?

If this is the case, then the code is horrible. Throwing an exception in .NET is extremely slow, and should never be thrown as a result of a normal situation. I repeat: "extremely slow"