SUMMARY
Folders that are clicked & dragged from the side panel ("Places") are moved to the place where they are dropped. If "Drag and Drop" in the settings (General Bahavior -> Drag and Drop) is set to "Move if on same device", dolphin will not even ask before moving it.

STEPS TO REPRODUCE
1. Open dolphin
2. Drag any folder from the "places" list to any other location
3. Click on the folder linked in "places" ... "annnddd It's Gone"

OBSERVED RESULT
If you click on the linked path in "places" the folder behind the link is *moved* to the location where the link is dropped. The link in the "Places" list itself stays in place. The (custom) icon of the folder is removed.

EXPECTED RESULT
DO NOTHING! (Literally do nothing. If you want to remove the link you can right click and use the context menu)
If I drag the link I may expect to remove the link from the "Places" list. I may expect to create a link to the folder. I would never expect that the folder is *moved*.

ADDITIONAL INFORMATION
Example video will be uploaded once rendering is finished.

I discovered this by accidentally moving the folder. As the folder just had the name, but no custom icon, I didn't think that the folder was *moved* as it doesn't make any sense to me. Because I did neither need a copy nor a linked version of the folder I (Shift + Delete)d the folder. A few seconds later I realised that the folder was not copied or linked and that the link in "Places" just gives me a red bar at the top and a friendly note that the path no longer exists. Thankfully the folder itself just contained linked files and folders so they are easy to restore. Now image if it was your homework folder!
Because the behaviour is so unexpected and just asks for serious trouble, I set the bug to "critical" even there is nothing 'broken'. Feel free to change the severity to a different level.
If there really is a need for this behaviour (which I kinda disagree) it should be an option that is OFF by default. If the option the bahaviour is optional but ON by default (which I *strongly* disagree with) the link should be removed from the list with drag&drop to at least indicate that you have just done something to the folder.

SOFTWARE/OS VERSIONS
Operating System: KDE neon User Edition
KDE Plasma Version: 6.4.4
KDE Frameworks Version: 6.17.0
Qt Version: 6.9.1
Kernel Version: 6.14.0-29-generic (64-bit)
Graphics Platform: Wayland
Processors: 12 × AMD Ryzen 5 7530U with Radeon Graphics
Memory: 32 GiB of RAM (29.2 GiB usable)
Graphics Processor: AMD Radeon Graphics
Manufacturer: LENOVO
Product Name: 21KK
System Version: ThinkBook 16 G6 ABP

Dolphin Version: 25.08.0