Contents of textarea outside updatepanel get posted when updatepanel does postback.

Hi,
I have some wierd problem that I can't seem to wrap my head around.
I have a page that holds a textarea. There is no updatepanel on the page, but the containing masterpage does have a updatepanel that is triggered every minute or so by a timer. It seems that every time the updatepanel is triggered, the contents of the textarea is send to the server and back. This is sort of a problem, since the contents of the textarea must be decoded first before it is send to the server in order to avoid a 500 server error (illegal characters). So I added in the page_load event the following statements:
ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "DecodeField", string.Format("<script>$(document).ready(function() {{ DecodeField('{0}'); DecodeField('{1}'); }});</script>", txtWWWintro.ClientID, txtWWWdescription.Clien ...