I don't think this ha been already reported, and I can't find the PEBCAO.
It's a minor display issue, but quite visible.
I got into the situation where an FFT, with horizontal span selected as Linear, is displayed with the right frequency labels, but a logaritmic (Decade) graticule.
Changing from/to Decade and Linear, or any other parameters, including turning off the Math channel and altering the formula did not solve the issue.
See below:

I had previously switched to Decade and then reverted to Linear, but that is not -in general- enough to trigger the problem.
The only way out I found was resetting the configuration to defaults, and starting over (in fact, reloading an older, similar, configuration).

I've saved (and attached) the problematic configuration, and reloading it shows the faulty display again.