JSFX "Reset to factory default" not working hidden sliders

[Erriez]

I'm developing a JSFX which contains several visible and hidden sliders. The hidden sliders are used to load/save values in a preset:

// Visible slider:
slider1:1<1,16,1>Channel

// Hidden slider with minus char in the name:
slider2:1<1,127,1>-Velocity

Load/save preset works for both.

"Reset to factory default" resets the visible sliders only and not the hidden sliders.

Is this a bug in Reaper v6.15 on Windows, or do I something wrong?