Nope. Viticellas have this tendency. They also lose their leaves at the bottom as the season progresses. Consider it normal.

You can plant some smaller plants in front of it to mask its legginess, including shorter, non-vining clematis integrifolias, or you can plant it through a tree or shrub so that you don't notice the bare parts.

I kept pinching mine after I hard pruned and not letting them grow as tall as they wanted and I do have blooms down lower than if I had not done this but still more than 50% are at the top of the trellis.

Ditto to what BorS said. The more you pinch earlier in the season, the lower on the stem the flowers will be. You still can't expect flowers all the way to the bottom of the stems however.