If the problem is the name for "Rue de l'Abbe Bovet" (you're most likely rendering the OSM data from here) is appearing twice, I don't think there's a problem with the data (it's a single object in OSM, see here but rather the renderer (mapnik/tilecache).
As suggested in the comments (by Michael Markieta) check your TextSymbolizer definitions. The relevant attribute is called
<Filter>[highway] = 'tertiary'</Filter>
<TextSymbolizer name="name" ... placement="line" spacing="500"/>
would cause tertiary road labels to be repeated every 500 pixels.
Another thing that may be worth tinkering with is mapnik's parameter called
buffer_size. I'm not sure how this works in tilecache (I've only used it in the python mapnik extensions).
As far as I remember what
buffer_size does is: whenever mapnik renders something it looks at whatever is rendered through a window of
buffer_size - if you want mapnik to realize it has to avoid painting a label because it's already there the label candidate and the already painted label have to coexist within the same rendering window.