Update: heartofhate indicated to me via PM that the problem resolved itself after a clean re-install.
(not to say that there isn't a bug, but rather that a workaround may be a clean install).

-Rusty

I have recently noticed this, too. The files all come from the same base folder with many subfolders. My setup is:

Drive://#Media/Shows And Demo/Decade/Year/Files

Files are in bunches and singles, all mp3 format, all have been tagged, over the years of collection, yet I have literally thousands of tracks that, to some extent, I have retagged over and over again. I just can't put a finger on why they are doing this.

1) I can't reproduce. Tried several times on different nodes in the Location node and it opened the Column Browser each time and showed all items.

2) My Computer node, Now Playing node/window or a Library node? I haven't seen missing tags before.

since i have updated to version 4.0.3 i have got a few weird things:
on the MM startup the coloumn browser won't load every artist and sometimes it will jump to one artist with no reason (mostly Rainbow). since i use the coloumn browser often this behauviour is really annoying.

also MM will just delete some tags of some files (at least they do not show up when i restart MM). this happened only twice to me.
the funny thing is that the tags are still there when i go to the properties.