Olddatastop error despite using lastwrite flag

[mcnbe]

I am programming an application with a 3D contour much like the buffered Rose example. Since I do not know the number of points to be written I have done the following:
1. Configure the buffer with a high number (240000) points.
2. When writing data to the buffer, I use regenerationmode_nochange when I know there is more data to come, I use regenerationmode_lastwrite when writing the last buffer.
3. Wait for the motion completed after writing the last buffer.

Now in my first test program I have just one buffer, so I immediately write a buffer using the lastwrite flag and then start the motion. So why do I get an olddatastop error?

[mcnbe]

I did some more testing and it does work with two buffer write operations. The first with regenerationmode_nochange and the followng with regenerationmode_lastwrite.
A single buffer write with regenerationmode_lastwrite is apparently not accepted by the system.