Overwriting original in annotation mode does not work

Steps to reproduce

1. Use Nextcloud Liquid for iOS 4.0.1.1
2. Open context menu of pdf file (three dots)
3. Select annotate(?)/change with the pencil icon in the circle (DE: Ändern)
4. Draw something in the document
5. Press Done and select overwrite original
6. Reopen the document to check if changes were saved
7. Be sad you lost 2h of annotations
   (Saving a copy works)

Expected behaviour

When overwriting the original, it should be writting to storage and nextcloud. Changes shouldn't disappear.

Actual behaviour

Nothing is saved, all is lost.

Reasoning or why should it be changed/implemented?

It means data loss, which is really frustrating and damaging to the perception of NC quality.

Environment data

iOS version: e.g. iOS 14.6

Nextcloud iOS app version: Nextcloud Liquid for iOS 4.0.1.1

Operating system: Linux 4.15.0-88-generic #88-Ubuntu SMP Tue Feb 11 20:11:34 UTC 2020 x86_64

Webserver: nginx/1.18.0 (fpm-fcgi) + nginx reverse proxy

Database: mysql 10.3.29

PHP version: 7.4.3

Modules loaded: Core, date, libxml, openssl, pcre, zlib, filter, hash, Reflection, SPL, session, standard, sodium, cgi-fcgi, mysqlnd, PDO, xml, apcu, bcmath, calendar, ctype, curl, dom, mbstring, FFI, fileinfo, ftp, gd, gettext, gmp, iconv, igbinary, imagick, intl, json, exif, mysqli, pdo_mysql, apc, posix, readline, redis, shmop, SimpleXML, sockets, sysvmsg, sysvsem, sysvshm, tokenizer, xmlreader, xmlwriter, xsl, zip, Phar, Zend OPcache

Nextcloud version: 21.0.2 - 21.0.2.1