The colon is an invalid character in Graphic Equalizer user preset names. If you type a colon in the name, no error message is generated. The preset is actually saved (in pluginsettings.cfg), but the name is corrupted and will not show up in the Graphic Equalizer user preset list - so you can not load or delete it.
Additionally, I found that if you escape the colon by editing pluginsettings.cfg then the preset will appear in the list (with the colon). But if you select it, the settings will not be loaded. Removing the escaped colon enables you to both select it and load it.
Generate an error message when user types an invalid preset name and don’t save the preset.
Note: I am a Senior Software Engineer (retired) and would like to help with QA testing.