Problem : Your vertex map is not updating at render time in R18 or R19.
Topo Vertex maps was built in R13.
Maxon made some changes in later versions which adversely effect the way the topo tag executes at render timer. The best solution to work around this problem is to use the render queue to render your animations. The queue still behave as it should, and vertex maps will update as expected, during a render, via the queue.