Newly created folder immediately contains copy of parent folder containing half of parent's folders moved to it

Version information

Thunar 4.20.2, Xubuntu 24.10

Steps to reproduce

In my data partition, /media/simon/data, create a new folder "Reinstall". (I previously had a folder there called "XubuntuReinstallBackupConfigs" but it was lost thanks to Timeshift being awful and causing the loss of loads of data. This may be irrelevant but since it contains the word "Reinstall" I thought I'd share this info just in case) Immediately within the expected-empty folder Reinstall, there's a subfolder 'data', which contains much of the contents which were previously in /data:

Subsequently various things like folder links are now broken, because e.g. /data/Documents is now in /data/Reinstall/data/Documents and thus /home/simon/Documents can't find its parent link.

The following confirms it's not a symlink:

/media/simon$ ls -l data
total 44
drwxrwxr-x  2 simon simon  4096 Jun 10 19:10 Downloads
drwx------ 22 simon simon  4096 Jun 11 07:20 Dropbox
drwx------  2 root  root  16384 Jan 24 19:24 lost+found
drwxr-xr-x 39 simon simon  4096 Jun 11 07:20 Music
drwxr-xr-x 40 simon simon  4096 Jun 11 07:20 Pictures
drwxrwxr-x  3 simon simon  4096 Jun 11 07:42 Reinstall
drwxr-xr-x  2 simon simon  4096 Mar 27 09:30 Templates
drwxrwxr-x  9 root  root   4096 Jun 10 09:00 timeshift

/media/simon/data/Reinstall$ ls -l data
total 52
-rw-rw-r-- 1 simon simon    67 Jan  3  2022  crash_log.txt
drwxr-xr-x 6 simon simon  4096 Feb 24 22:25  Documents
drwxrwxr-x 5 simon simon  4096 Jun 11 07:20  Programs
drwxr-xr-x 2 simon simon  4096 Jan 26  2021  Public
drwxrwxr-x 3 simon simon  4096 Jan 26  2021  R
-rw-rw-r-- 1 simon simon   299 Feb  3  2021  settings.txt
drwx------ 8 simon simon  4096 Jun 24  2024  snap
-rw-rw-r-- 1 simon simon 17015 Jun 10 22:23 'todo list new PC setup.txt'
drwxr-xr-x 2 simon simon  4096 Jan 21 18:34  Videos

Nor is it a mount bind:

/media/simon$ mount | grep /data
/dev/nvme1n1p3 on /media/simon/data type ext4 (rw,nosuid,nodev,relatime,x-gvfs-show,x-gvfs-name=data,x-gvfs-icon=drive-harddisk)

/media/simon$ findmnt | grep /data
└─/media/simon/data                                           /dev/nvme1n1p3         ext4            rw,nosuid,nodev,relatime

I'm concerned that these phantom moving/copying/linking behaviours occur seemingly without request or intent or warning, and efforts to correct them are fraught with huge risk of data loss, breaking packages, etc.

Relatedly I have no idea why there are so many hidden files in /data since I never created them. In /data/Reinstall/data they sum to 56gb, in /data another 1gb. Inevitably these are vital to crucial system functions but I explicitly created the /data partition to avoid having system files there, yet here they are. Naturally I'm not going to delete them since I'm sure it'll brick my system. I just don't know how my setup is getting so scrambled when I'm spending so much time and effort explicitly trying to avoid this exact scenario.

Any advice very much welcome (especially: whether I can just move those folders back from data/Reinstall/data to /data). Thanks gents, hope you're well.