Only problem is when you try to use that virtual rag in a playlist or for highlighting, MB becomes unresponsive, eventually needing to shutdown and restarted.
i don't think it's a bug. mostly likely it's just slow. i can re-enable LR function result caching in the plugin (i've commented out this code because MB-native caching is working fine for me), but i'm not sure if it improves situation significantly. do you consider this issue important?
p.s. it's much better to calculate LR functions at startup, saving their results to custom tags to avoid freezes and slowdowns.
btw, i understand what you mean by "use virtual tag for highlighting", but what do you mean by "use virtual tag for playlist"? auto-playlists?