It all revolves around the "&" symbol in the url's of trailers. MythTV will not accept button code that looks like this:

<button>
<type>MOVIETIMES</type>
<text>Amusement</text>
<action>EXEC xine -f -S --no-splash --no-logo http://playlist.yahoo.com/makeplaylist.dll?sdm=web &pt=rd&sid=49083905 </action>
</button>

But it will take it when I leave the special symbol html substitution code in like this:

<button>
<type>MOVIETIMES</type>
<text>Amusement</text>
<action>EXEC xine -f -S --no-splash --no-logo             http://playlist.yahoo.com/makeplaylist.dll?sdm=web&amp;pt=rd&amp;sid=49083905 </action>
</button>