Szenario:

1. Physical full backup with mariadb-backup (--backup)
2. Prepare of this backup (--prepare)
3. Prepare with export for partial physical restore (--prepare --export --database=test)
4. DISCARD/cp/chown/IMPORT of tablespace
Up to here everything is fine. NO DB restart is done.
5. Physical full backup with mariadb-backup (--backup) again.

*.ibd file is missing in backup:
rw-rw--- 1 mysql mysql 65 Jun 18 17:33 /tmp/bck/daily/bck_full_2024-06-18/test/db.opt
rw-rw--- 1 mysql mysql 1100 Jun 18 17:33 /tmp/bck/daily/bck_full_2024-06-18/test/test.frm

and we get in mariadb-backup output the following message:

...
[00] 2024-06-18 17:33:02 mariabackup: Generating a list of tablespaces
[00] 2024-06-18 17:33:02 DDL tracking : delete 1595 "./test/test.ibd"
...
[01] 2024-06-18 17:33:05 Warning: We assume the table was dropped during xtrabackup execution and ignore the tablespace ./test/test.ibd
...
[00] 2024-06-18 17:33:20 Redo log (from LSN 52224057258 to 52224510260) was copied.
[00] 2024-06-18 17:33:20 completed OK!

That means, that this backup is broken now an cannot be used for future partial or full restore!!!

Steps to reproduce:

PORT=3321
DATADIR=/home/mysql/database/mariadb-1011/data
BACKUPNAME=bck_full_2024-06-18
BACKUPDIR=/tmp/bck

rm -rf ${BACKUPDIR}/daily/${BACKUPNAME}

/home/mysql/product/mariadb-10.11/bin/mariabackup --user=brman --password=secret --host=127.0.0.1 --port=3321 --backup --target-dir=/tmp/bck/daily/bck_full_2024-06-18
/home/mysql/product/mariadb-10.11/bin/mariabackup --user=brman --password=secret --host=127.0.0.1 --port=3321 --prepare --target-dir=/tmp/bck/daily/bck_full_2024-06-18
/home/mysql/product/mariadb-10.11/bin/mariabackup --user=brman --host=127.0.0.1 --port=3321 --prepare --export --databases=test --target-dir=/tmp/bck/daily/bck_full_2024-06-18

ALTER TABLE `test`.`test` DISCARD TABLESPACE;
cp /tmp/bck/daily/bck_full_2024-06-18/test/test.cfg /home/mysql/database/mariadb-1011/data/test/test.cfg
cp /tmp/bck/daily/bck_full_2024-06-18/test/test.ibd /home/mysql/database/mariadb-1011/data/test/test.ibd
chown mysql: /home/mysql/database/mariadb-1011/data/test/test.cfg /home/mysql/database/mariadb-1011/data/test/test.ibd
ALTER TABLE `test`.`test` IMPORT TABLESPACE;
rm /home/mysql/database/mariadb-1011/data/test/test.cfg
rm /tmp/bck/daily/bck_full_2024-06-18/test/test.cfg

no restart

/home/mysql/product/mariadb-10.11/bin/mariabackup --user=brman --password=secret --host=127.0.0.1 --port=3321 --backup --target-dir=/tmp/bck/daily/bck_full_2024-06-18