This can be fixed in the mod-ui client. Ugly, but it works 
Following will put MIDI plugins to the MIDI category and unknown plugins to a new category called Other.
Modifiy /usr/share/mod/html/index.html
and add following lines to the div called plugin-results-wrapper:
<div id="plugin-results-wrapper">
(...)
<div id="effect-content-MIDIPlugin" class="plugins-wrapper"></div>
(...)
<div id="effect-content-Other" class="plugins-wrapper"></div>
(...)
</div>
and add following li’s to the js-category-tabs ul:
<ul class="clearfix js-category-tabs">
(...)
<li id="effect-tab-MIDIPlugin">MIDI</li>
(...)
<li id="effect-tab-Other">Other</li>
(...)
</ul>
In /usr/share/mod/html/js/effects.js
modify the function renderNextPlugin thats embedded in the showPlugins function to:
function renderNextPlugin(c) {
if (self.data('showPluginsRenderId') != currentRenderId) {
// another render is in place, stop this one
if (callback) { callback() }
return
}
if (renderedIndex >= pluginCount) {
// if we get here it means we finished rendering
self.effectBox('calculateNavigation')
if (self.data('showPluginsRenderId') == currentRenderId) {
// no other renders in queue, take the chance and reset the id
self.data('showPluginsRenderId', 0)
}
if (callback) { callback() }
return
}
plugin = plugins[renderedIndex]
category = plugin.category[0]
self.effectBox('renderPlugin', plugin, self.find('#effect-content-All'))
if (FAVORITES.indexOf(plugin.uri) >= 0) {
self.effectBox('renderPlugin', plugin, self.find('#effect-content-Favorites'))
}
if(!category){
category = (plugin.label.match(/MIDI/gi) || plugin.name.match(/MIDI/gi)) ? "MIDIPlugin" : "Other";
}
if (category && category != 'All') {
self.effectBox('renderPlugin', plugin, self.find('#effect-content-' + category))
}
renderedIndex += 1
c = c || 0;
if (c < 20) renderNextPlugin(c+1);
else setTimeout(renderNextPlugin, 1);
}
Don’t know how to highlight code, so put this:
if(!category){
category = (plugin.label.match(/MIDI/gi) || plugin.name.match(/MIDI/gi)) ? "MIDIPlugin" : "Other";
}
before:
if (category && category != 'All') {
self.effectBox('renderPlugin', plugin, self.find('#effect-content-' + category))
}