In RME gives the same problem.I recommend remere map editor.
<house name="Small Street IV">
<tile x="146" y="43" z="6"/>
<tile x="146" y="44" z="6"/>
<tile x="146" y="45" z="6"/>
</house>
<house name="Small Street V">
<tiles fromx="143" fromy="43" fromz="5" tox="144" toy="45" toz="5"/>
</house>
<?xml version="1.0"?>
<house><frontdoor x="134" y="61" z="7"/><owner name=""/></house>
In RME gives the same problem.