file1.flac is 623 MB
file2.flac is 180 MB
combined.flac is 991 MB, 188 MB or 23% bigger. What am I doing wrong?

I have XP and FLAC 1.1.4, level -8. I have encoded these files twice, to make sure I didn't inadvertently encode w/ different level. I have also decoded the flac back to WAV and compared (w/ EAC), and they are the same.

This only happened w/ one album, Wagner's "Tristan und Isolde" conducted by Furtwangler released 2004. There have been several re-releases and remastering of this recording, and so to reproduced this problem you will need the 2004 release.

I have done this w/ 4 or 5 other albums, no problem, i.e. the discrepancies are less than 5 MB, which is a lot less than 188 MB.

I am completely stumped.

I think there are two problems:

1) I am using Audacity to join the files, and I cannot get Audacity to join correctly (see topic
howto perfectly join 2 wav's in Audacity?)

2) The tracks are in mono. Audacity joins the stereo tracks incorrectly. However, FLAC encodes them more or less the same size. It is only w/ these mono tracks where FLAC compression increases 10-25%.