Just tested it and you're wrong (at least for MKV files).
I had a MKV file imported into MC (
12.0.396 so if the change was in the last two builds then I apologize I re-tested with 398 and it was the same). It was manually tagged to this:
[Name] = The Hudsucker Proxy
[Album] = <blank>
[Filename] = M:\Incoming\The Hudsucker Proxy.mkv
Forcing Update Library (from Tags) changed it to this (it did rebuild the thumbnail):
[Name] = Done with AutoMKV 0.84b
http://forum.doom9.org/showthread.php?p=854221[Album] = blank
[Filename] = M:\Incoming\The Hudsucker Proxy.mkv
The file info is:
General #0
Complete name : M:\Incoming\The Hudsucker Proxy.mkv
Format : Matroska
File size : 1.50 GiB
PlayTime : 1h 50mn
Bit rate : 1936 Kbps
Movie name : Done with AutoMKV 0.84b http://forum.doom9.org/showthread.php?p=854221
Encoded date : UTC 2007-06-01 01:47:15
Writing application : mkvmerge v2.0.2 ('You're My Flame') built on Feb 21 2007 23:40:55
Writing library : libebml v0.7.7 + libmatroska v0.8.1
Video #0
Codec : MPEG-4 AVC
Codec/Info : MPEG4 ISO advanced profile
PlayTime : 1h 50mn
Width : 720 pixels
Height : 544 pixels
Aspect ratio : 4/3
Frame rate : 23.976 fps
Title : The Hudsucker Proxy
Audio #0
Codec : A_AAC
Channel(s) : 2 channels
Sampling rate : 48 KHz
This is obviously not safe. Even those MKV files I have that weren't encoded with AutoMKV, often have incorrect file tag information embedded. Since MC doesn't fix the file tags, forcing an update causes MC to ruin it's own tags... Obviously this would not be very effective when my goal is to be able to open a View Scheme showing
all MKV files (when I have 30 or 40 missing thumbnails) and do Control-A, right click, Fix Thumbnail.
EDIT: Even worse, I noticed that you can't "undo" this operation. So, once they're all messed up, your only option would be to manually go through and re-tag them!