no sera la funcion autocomplete, mira estos dos formularios y veras que no los completa
<form method="GET" action="buscar.htm">
<p><input type="text" name="buscar" size="20" autocomplete="off"><input type="submit" value="Enviar" name="B1"></p>
</form>
<form method="GET" action="buscar.htm">
<p><input type="text" name="buscar" size="20"><input type="submit" value="Enviar" name="B1"></p>
</form>