A question about filename generate

[safreya <safreya@xxxxxx>]

I'm confused about ** expansion.In the following example:

safreya test % ls --tree
Permissions Size User    Group   Date Modified Name
drwxr-xr-x     - safreya safreya 27 Jul 13:03   .
drwxr-xr-x     - safreya safreya 27 Jul 13:02  ├──  subdir
.rw-r--r--     0 safreya safreya 27 Jul 13:02  │   ├──  filea.aux
.rw-r--r--     0 safreya safreya 27 Jul 13:02  │   ├──  filea.tex
.rw-r--r--     0 safreya safreya 27 Jul 13:02  │   ├──  fileb.aux
.rw-r--r--     0 safreya safreya 27 Jul 13:02  │   ├──  fileb.tex
.rw-r--r--     0 safreya safreya 27 Jul 13:02  │   ├──  filec.aux
.rw-r--r--     0 safreya safreya 27 Jul 13:02  │   └──  filec.tex
.rw-r--r--     0 safreya safreya 27 Jul 13:03  ├──  index.aux
.rw-r--r--     0 safreya safreya 27 Jul 13:03  ├──  index.log
.rw-r--r--     0 safreya safreya 27 Jul 13:03  └──  index.tex
safreya test % setopt extendedglob
safreya test % print -l **/*~**/*.tex
index.aux
index.log
index.tex
subdir
subdir/filea.aux
subdir/fileb.aux
subdir/filec.aux

I notice that index.tex is printed. This means:

1. The first ** expansion include index.tex
2. The second ** expansion not

Why?

I made this example with FreeBSD zsh 5.9.