Unexpected behavior with ExtendedData Element

[j...@sierrajoes.com]

I added an ExtendedData element to one of a kml file's placemark
elements. When I opened the file in google Earth, That one placemark
behaved differently than all the others in the file. The placemark
with the ExtendedData element opened an information window (bubble)
when clicked with the placemark name and a directions: To here - From
here set of links.

In accordance with the kml documentation, I used a unique namespace so
expected Earth to completely ignore this element. However, it
obviously did not completely ignore its presence.

Here is the placemark xml excerpt with the ExtendedData element:

<Placemark>
<name>Start/End</name>
<styleUrl>#msn_grn-square</styleUrl>
<!-- Imported schema requires use of namespace prefix -->
<ExtendedData xmlns:geoxml="http://www.dyasdesigns.com/geoxml/">
<geoxml:plywood>1</geoxml:plywood>
</ExtendedData>

<Point>
<coordinates>-120.259558,38.251056,1348.845215</coordinates>
</Point>
</Placemark>

here, plywood is completely meaningless.
joe