Smoothing of a constant plot is messed up

When I try to smooth a value which is constant, then some strange spikes appear in the plot.
For example:

Here actor_learn_rate is always a constant. Interestingly, in its own tab it is displayed correctly, but in the Tags matching tab it is messed up. When I hover over the plot at a point corresponding to a spike, the correct value of 1e-4 is reported. The case is the same for critic_learn_rate.

Interestingly, the spikes depend on the smoothing value. For example, for a smoothing value of 0.222, there are no spikes:

However, the orange line is not displayed at 1e-4 which is the correct value.

Then a smoothing value of 0 is the same.

My version is tensorflow-tensorboard (0.4.0rc3)