Removing old kernels with zypper increases the disk usage

I have updated my Suse Tumbleweed system, and consequently a new kernel version has been installed. To reclaim space used by an _ancient_ kernel, I decided to use the zypper purge-kernels command, and here it is what happened:

$ df / ; sudo zypper purge-kernels ; df /
Filesystem              1K-blocks     Used Available Use% Mounted on
/dev/mapper/system-root  36700160 27053812   8861788  76% /
[sudo] password for root: 
Reading installed packages...

Preparing to purge obsolete kernels...
Configuration: latest,latest-1,running
Running kernel release: 6.15.4-1-default
Running kernel arch: x86_64

Resolving package dependencies...

The following 3 packages are going to be REMOVED:
  bbswitch-kmp-default-0.8_k6.15.3_2-14.42 kernel-default-6.15.3-2.1
  ovpn-dco-kmp-default-0.2.20241216~git0.a08b2fd_k6.15.3_2-3.17

3 packages to remove.

Package install size change:
              |         0 B    required by packages that will be installed
  -258.5 MiB  |  -  258.5 MiB  released by packages that will be removed

Backend:  classic_rpmtrans
Continue? [y/n/v/...? shows all options] (y): 
(1/3) Removing: bbswitch-kmp-default-0.8_k6.15.3_2-14.42.x86_64 ..............[done]
(2/3) Removing: ovpn-dco-kmp-default-0.2.20241216~git0.a08b2fd_k6.15.3_2-3.17.[done]
(3/3) Removing: kernel-default-6.15.3-2.1.x86_64 .............................[done]
Running post-transaction scripts .............................................[done]
There are running programs which still use files and libraries deleted or updated by recent upgrades. They should be restarted to benefit from the latest updates. Run 'zypper ps -s' to list these programs.
 
Since the last system boot core libraries or services have been updated.
Reboot is suggested to ensure that your system benefits from these updates.
Filesystem              1K-blocks     Used Available Use% Mounted on
/dev/mapper/system-root  36700160 27463068   8455604  77% /
$

After releasing 258.5 MiB of disk space, I end up with an increased occupation of 397 KiB. I suspect that Suse saves the data somewhere and for good measure adds some book-keeping stuff, but I'd like a confirmation of these suspects and also 1. an explanation of this behavior (if you need more detail, as usual ask in comments), 2. how can I prevent such behavior. --- _Addendum_ I tried rebooting, to see if some disk space was held away from running processes, but I found that it was not my case.