It seems that the starttimes of traces are not handled correctly when writing to Q-files using the st.write(file, format='Q') and when the starttime of the trace is before 1970.
In this case 100 years are added to the starttime in the output file, e.g. 1969,12,31 --> 2069,12,31.
I am using obspy 0.10.
Dirk