istream: seekg / tellg, peculiar behaviour

[LiquidEyes]

I'm having two istream-related problems. Please can somebody help... :confused: Problem 1

void loadStuffFromStream (istream& stream)
{
	// goes too far!!
	stream.seekg( length, ios_base::cur );
}

***edited*** This seems to skip to an arbitrary position in the stream, instead of 'current position' + length bytes. Why does it do this? Problem 2

char ch;
int pos;
...
pos = stream.tellg();		// now pos=0
stream.get (ch);
pos = stream.tellg();		// now pos=3585 ???
stream.get (ch);
pos = stream.tellg();		// now pos=3586
stream.get (ch);
pos = stream.tellg();		// now pos=3587
stream.get (ch);
// etc...

Not so much a 'problem' as a matter of curiosity. Why is there a sudden leap in the read-position reported by tellg the first time I read from the stream? (N.B. It is reading the correct characters into ch!)