@jimp:
Did you adjust the gateway preferences for "Frequency Probe" on that gateway? Read the note next to that field.
I currently don't have any of the advanced things set (I did, but had never overridden the probe frequency). The top graph shows "Quality - 3 hours - 1 minute averages", but it is clearly drawn only every 5 minutes, and the graph shows that they are definitely in chunks (looks more like a bar-graph than a line-graph)
rrd-q.png_thumb
rrd-q.png