When I wrote "modifying its source code", I was thinking at the four freedoms of free software...
GPL3:
"Therefore, you have
certain responsibilities if you distribute copies of the software, or if
you modify it: responsibilities to respect the freedom of others."
" For the developers' and authors' protection, the GPL clearly explains
that there is no warranty for this free software. For both users' and
authors' sake, the GPL requires that modified versions be marked as
changed, so that their problems will not be attributed erroneously to
authors of previous versions."
Clearly, some people forgot to mark as changed and add their name
to their modifications/regressions to my source code.
"""
To "modify" a work means to copy from or adapt all or part of the work
in a fashion requiring copyright permission, other than the making of an
exact copy. The resulting work is called a "modified version" of the
earlier work or a work "based on" the earlier work.

A "covered work" means either the unmodified Program or a work based
on the Program.

To "propagate" a work means to do anything with it that, without
permission, would make you directly or secondarily liable for
infringement under applicable copyright law, except executing it on a
computer or modifying a private copy.
"""
Moreover, maybe some people think
that reverting and destroying parts of the commits (history)
is not a modification since it is just a "time-travel" ???
Another fun fact:
I remember reading in a "previous version" of GPL3,
that it was needed to add your name when distributing modifications, etc.
I also think that the following precisions would be welcome:
You are not authorized to modify the history of a V.C.S. of a program under (L.)G.P.L.,
and in case you contribute, you should not impersonate someone else as the commiter.
If you want a "clean branch" for didactic purposes,
with commits reordered, merged, squashed, destroyed, bugless, full of bugs,
and present a "nice" history,
you should name it with a prefix cleaned-history...
and leave the main/master/dev/etc. other branches untouched.