DISCTOTAL tag being discarded for TOTALDISCS
I've mapped my "total discs" tag in the "advanced" -> "display" -> "properties dialog" -> "standard fields" setting to DISCTOTAL (as proposed for Vorbis tags by Xiph). However, this tag gets replaced by TOTALDISCS when anything reloads/updates the tags (even just by the built-in context menu -> tagging -> reload tags function). I thought this may have been a problem with foo_playback_custom (which is how I initially noticed the behavior, since it updates a PLAYCOUNT tag on track end), or some sort of caching bug. But even after a clean start followed directly by executing "reload tags" on a file, it still does the same thing. Now I've just checked a file in a hex editor, and I actually don't see the TOTALDISCS tag present anywhere. So it seems like it's replaced in some form of fb2k's parsed tags only.. ?

These are the only components I have installed:
Core (2015-11-02 13:34:32 UTC)
foobar2000 core 1.3.9
foo_ac3.dll (2013-02-28 02:21:29 UTC)
AC3 decoder 0.9.7
foo_acm_packet_decoder.dll (2014-05-16 20:57:56 UTC)
ACM Packet Decoder 0.0.1
foo_adpcm.dll (2015-02-23 21:33:35 UTC)
kode's ADPCM decoders 1.11
foo_cdda.dll (2015-11-02 13:30:24 UTC)
CD Audio Decoder 3.0
foo_converter.dll (2015-11-02 13:30:32 UTC)
Converter 1.5
foo_dsp_effect.dll (2015-04-03 04:24:09 UTC)
Effect DSP 0.16
foo_dsp_eq.dll (2015-11-02 13:30:52 UTC)
Equalizer 1.0
foo_dsp_resampler.dll (2013-12-15 10:56:08 UTC)
SoX Resampler 0.8.3
foo_dsp_std.dll (2015-11-02 13:30:38 UTC)
Standard DSP Array 1.3.1
foo_dumb.dll (2015-11-15 01:14:08 UTC)
DUMB module decoder 1.0.158
foo_fileops.dll (2015-11-02 13:30:04 UTC)
File Operations 2.2.1
foo_flv.dll (2013-08-24 23:19:09 UTC)
Flash Video Decoder 0.9.6
foo_gep.dll (2015-12-28 18:46:05 UTC)
Game Emu Player 1.193
foo_input_amr.dll (2014-11-04 12:58:28 UTC)
AMR 输入 1.1.1
foo_input_aodsf.dll (2013-02-28 02:22:24 UTC)
DSF decoder / Audio Overload SDK 1.4.8u3 0.10
foo_input_caf.dll (2014-05-15 11:50:39 UTC)
CAF Decoder 0.0.10
foo_input_dts.dll (2014-06-10 01:25:33 UTC)
DTS decoder 0.3.3
foo_input_mdx.dll (2013-02-28 01:59:12 UTC)
MDC input 1.0.1
MDX input 1.1.0
foo_input_monkey.dll (2013-05-24 13:21:18 UTC)
Monkey's Audio Decoder 2.1.7
foo_input_std.dll (2015-11-02 13:34:32 UTC)
Standard Input Array 1.0
foo_input_tak.dll (2013-10-13 03:38:21 UTC)
TAK Decoder 0.4.7
foo_input_tta.dll (2013-02-28 01:59:12 UTC)
TTA Audio Decoder 3.0
foo_input_usf.dll (2015-05-31 14:47:58 UTC)
LazyUSF 2.2.39
foo_input_vgmstream.dll (2015-10-13 14:23:26 UTC)
vgmstream plugin r1050-32-gec99511
foo_midi.dll (2015-10-13 14:23:26 UTC)
MIDI synthesizer host 1.247
foo_playback_custom.dll (2013-06-08 01:56:52 UTC)
Playback Statistics Custom 1.5.1
foo_psf.dll (2015-10-13 14:23:26 UTC)
AOPSF 2.1.9
foo_quicktag.dll (2013-06-08 01:01:34 UTC)
Quick Tagger 1.0.3
foo_rgscan.dll (2015-11-02 13:31:02 UTC)
ReplayGain Scanner 2.2.2
foo_skip.dll (2015-02-01 23:16:05 UTC)
Skip Track 1.9.7
foo_texttools.dll (2013-02-28 01:59:12 UTC)
Text Tools 1.0.5
foo_ui_std.dll (2015-11-02 13:34:32 UTC)
Default User Interface 0.9.5
foo_unpack.dll (2015-11-02 13:30:38 UTC)
ZIP/GZIP/RAR Reader 1.7.1
foo_verifier.dll (2014-09-30 22:35:38 UTC)
File Integrity Verifier 1.1.2
foo_wave_seekbar.dll (2014-02-16 11:07:57 UTC)
Waveform seekbar 0.2.45
foobar2000 v1.3.9 on XP SP3.