Per its usage statement, kafka-console-consumer.sh ignores --from-beginning when the specified consumer group has committed offsets, and sets auto.offset.reset to latest. However, if --partition is also specified, --from-beginning is observed in all cases, whether there are committed offsets or not.
This happens because when --from-beginning is specified, offsetArg is set to OffsetRequest.EarliestTime. However, offsetArg is only passed to the constructor for NewShinyConsumer when --partition is also specified. Hence, it is honored in this case and not the other.
This case should either be handled consistently, or the usage statement should be modified to indicate the actual behavior/usage.