Query returns different number of results depending on fetchsize

I issue a query across the set of partitioned wide rows for one logical row, where s, l, and partition specify the composite primary key for the row:
SELECT ec, ea, rd FROM sr WHERE s = ? and partition IN ? and l = ? ALLOW FILTERING;

If I set fetchSize to only 1000 when the Cluster is configured, the query sometimes does not return all the results. In the particular case I am chasing, it returns a total of 98586 rows. If I increase the fetchsize to 100000, all the 99999 actual rows are returned. This suggests there is some problem with fetchsize re-establishing the position on the next segment of the result set, at least when multiple partitions are being accessed.