1) using a library on a SUBST drive - MC may have problems there
I use only substed local or mapped network drives. I use substed drives for creating my standard drive letters on any PC independently of the actual drive letters. I have not seen any problems. (Though I usually keep the background importer disabled and run auto-import by starting it manually.)
For instance, when I mount my two external media hard drives on my laptop I run four SUBST commands from a bat file. That creates the W:, X:, Y: and Z: drive letters that are referenced in my MC library.
When I use the same database on LAN I map the server shares and create the same W:, X:, Y:, and Z: letters.
2) deleting a playlist - MC fails to spot this
As discussed in the other threat, this is intentional, not a bug. You can request different functionality.
3) deleting a tag frame - again MC fails to spot this. Anyone know a workaround?
This is intentional, not a bug. MC doesn't constantly read the file tags and compare them with the database field values. It only imports all tag values if it is set to monitor changed files.
Also, the database fields don't have any stored attributes that could tell if the field originally existed in the file tags. One of the great things in MC is its capability to store all kinds of data in its database independently of the possibly existing support for physical file tags. (The tagging support varies greatly from a file type to another. Some can store any custom tags, some can store only certain tags and/or only limited tag values, and some cannot store tags at all.)
If you want use an external tagger a workaround could be to tag the files with a value like
#remove# instead of removing the tag. Then you could use the Find and Replace tool for replacing all
#remove# values in all tags in all files with nothing (i.e. use empty "Replace:" box in the tool's settings).
Now, a test on C: by adding a WMA file does succeed, albeit with a mysterious delay, suggesting MC is not ising the Windows immediate FS change notify mechanism that you'd expect, but instead slowly polling. I'll have to work out the boundary of working fucntionailty and see if I can live inside it.
I have seen some sluggishness in the background auto-importer. In addition to occasional slow detection of new files the automatic thumbnail creation can sometimes take very long (and I am not speaking about CPU intensive video thumbnailing, just standard audio importing).
Personally, I usually keep the background importer switched off and simply press the "Run Auto-Import Now" button on the top toolbar at a preferred time. (The button can be added there.)