Oracle OCCI stmt.setTimestamp insert TIMESTAMP(6): microseconds always 0
Turns out the "fractional seconds" field is nominally in nanoseconds rather than hundredths. I wish Oracle would say that in their documents! I say nominally because if it really preserved the least-significant digits then the hundredths values I had would have appeared as a number of nanoseconds and I might have immediately guessed at the problem - instead it seems values < 100 nanoseconds are lost anyway (and perhaps bigger - I haven't probed the cut-off point).
Thanks to anyone who had a look at the question or tried some research / investigation.