Melda VST3 still a problem here on 5.70 x32 running on win10 x64
Saving presets is ok but when you exit and load the plugin again and select the preset it will load, but immediately afterwards the '0' preset is automatically selected (even though it doesn't actually load) meaning you can no longer delete it.
The workaround is that if you save and overwrite the original preset it sticks (until you reload the plugin) meaning you can then delete it if you want to .. a bit error prone/inconvenient though
Tested on VST3 of MEqualizer and MBandPass.