bug#55272: 28.1; python-mode cannot delete or backspace when unmarked

[Castix]

Report generated from a fresh clone of python-mode, with  emacs -Q -l 
python-mode.el

Brief description of the bug:

I can't delete text unless it was previously marked.

I am adding as a reply to

https://gitlab.com/python-mode-devs/python-mode/-/issues/121#note_936095450

git log -1 says
```
commit f633c00233104d506fe2801d00f1430110ca5cdc (HEAD -> master, 
origin/master, origin/HEAD)
Author: Andreas Roehler <andreas.roehler@online.de>
Date: Wed May 4 20:29:34 2022 +0200

#119, py-up doesn't exist

fixed

```


please see the issue on gitlab for additional context


Thank you





In GNU Emacs 28.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.33, 
cairo version 1.17.6)
of 2022-04-28 built on frederik
Windowing system distributor 'The X.Org Foundation', version 11.0.12101003
System Description: Arch Linux

Configured using:
'configure --sysconfdir=/etc --prefix=/usr --libexecdir=/usr/lib
--localstatedir=/var --with-cairo --with-harfbuzz --with-libsystemd
--with-modules --with-x-toolkit=gtk3 'CFLAGS=-march=x86-64
-mtune=generic -O2 -pipe -fno-plt -fexceptions -Wp,-D_FORTIFY_SOURCE=2
-Wformat -Werror=format-security -fstack-clash-protection
-fcf-protection -g -ffile-prefix-map=/build/emacs/src=/usr/src/debug
-flto=auto' 'LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now
-flto=auto''

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY INOTIFY
PDUMPER PNG RSVG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE
XIM XPM GTK3 ZLIB

Important settings:
value of $LANG: en_US.UTF-8
locale-coding-system: utf-8-unix

Major mode: Py

Minor modes in effect:
outline-minor-mode: t
shell-dirtrack-mode: t
tooltip-mode: t
global-eldoc-mode: t
show-paren-mode: t
electric-indent-mode: t
mouse-wheel-mode: t
tool-bar-mode: t
menu-bar-mode: t
file-name-shadow-mode: t
global-font-lock-mode: t
font-lock-mode: t
blink-cursor-mode: t
auto-composition-mode: t
auto-encryption-mode: t
auto-compression-mode: t
line-number-mode: t
transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
rfc822 mml mml-sec epa epg rfc6068 epg-config gnus-util rmail
rmail-loaddefs mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils noutline outline easy-mmode python-mode
derived info-look info advice edmacro kmacro pcase rx org-loaddefs
tramp-sh tramp tramp-loaddefs trampver tramp-integration files-x
tramp-compat parse-time iso8601 time-date ls-lisp format-spec
auth-source cl-seq eieio eieio-core cl-macs eieio-loaddefs
password-cache which-func imenu shell pcomplete json map hideshow
hippie-exp flymake-proc flymake project seq byte-opt gv bytecomp
byte-compile cconv warnings thingatpt ert pp ewoc debug backtrace
help-mode find-func compile text-property-search comint ring cc-cmds
cc-engine cc-vars cc-defs cl-loaddefs cl-lib subr-x ansi-color
iso-transl tooltip eldoc paren electric uniquify ediff-hook vc-hooks
lisp-float-type elisp-mode mwheel term/x-win x-win term/common-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list replace
newcomment text-mode lisp-mode prog-mode register page tab-bar menu-bar
rfn-eshadow isearch easymenu timer select scroll-bar mouse jit-lock
font-lock syntax font-core term/tty-colors frame minibuffer cl-generic
cham georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese composite emoji-zwj charscript
charprop case-table epa-hook jka-cmpr-hook help simple abbrev obarray
cl-preloaded nadvice button loaddefs faces cus-face macroexp files
window text-properties overlay sha1 md5 base64 format env code-pages
mule custom widget hashtable-print-readable backquote threads dbusbind
inotify lcms2 dynamic-setting system-font-setting font-render-setting
cairo move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 195630 12936)
(symbols 48 15461 1)
(strings 32 45282 1931)
(string-bytes 1 1767448)
(vectors 16 23509)
(vector-slots 8 283725 16437)
(floats 8 72 16)
(intervals 56 273 0)
(buffers 992 10))