Chapter names are not being setup correctly.

[jbuddha]

I have a bunch of MP3 files in a folder with names such as these.

Their individual mp3 file's title tag is also set as Unit 01, Unit 02 etc., I tried to run following commands once with --use-filenames-as-chapters and once without using that flag.

m4b-tool merge "." --debug --output-file="Italian L1.m4b" --artist=X --skip-cover --name="Italian L1" --use-filenames-as-chapters

m4b-tool merge "." --debug --output-file="X Italian L1.m4b" --artist=X --skip-cover --name="X Italian L1"

In both cases, my chapters titles are not using the file name or title tag and producing following output in chapters section. How can I have the chapter names as Unit 01, Unit 02 etc? Right now, the only way I can think of solving this problem is run above command once, copy the chapters meta data output and create chapters.txt manually and delete generated temp files, and generated m4b and rerun the above command to generate final m4b file to have correct chapter names. The tool is great except for this minor issue I'm unable to solve.

chapters         
## total-duration:: 15:26:06.229
00:00:00.000 1.1
00:27:54.654 2.1
00:55:37.838 3
01:23:46.517 4
01:52:28.346 5
02:21:59.468 6
02:50:39.155 7
03:19:52.278 8
03:48:04.510 9
04:17:55.145 10
04:46:19.942 11
05:14:42.074 12
05:42:37.535 13
06:12:59.543 14
06:42:08.931 15
07:10:23.070 16
07:39:43.952 17
08:09:08.021 18
08:38:47.528 19
09:07:25.150 20
09:34:03.656 21
10:02:46.477 22
10:31:20.286 23
11:01:36.365 24
11:28:42.795 25
11:55:49.956 26
12:22:18.482 27
12:52:08.151 28
13:19:45.222 29
13:47:04.190 30
14:13:03.981 1.2
14:52:37.774 2.2

Can you tell what I'm doing incorrectly here?