Luci-app-statistics: conflicting graph data

WRT1900AC v1 (mamba) with Marvell Armada XP
OpenWRT built from snapshot r16521-a3c7633ddc
kernel: CPU frequency scaling enabled, on-demand governor, idle disabled (driver not built).

I'm getting these graphs in luci-app-statistics:

As you can see, there is a conflict between Processor frequency graph and Frequency distribution graph.

How can a CPU stay 99% at 0.6 GHz, yet the Frequency graph show 99% 1.2GHz ??
I think the collectd causes a frequency increase when it gathers the data and this is why Frequency graph shows false data.
I don't think there is any way to fix that graph. It should be removed, also from Overview tab, in favor of Frequency distribution graph which shows correct data.