Until now I - and likely other members - percieved this as an issue using two separate mounts as per your title
Cannot move files between SMB shared folders with Dolphin
With Linux you don’t always get a fix - but have to learn to work around it - such as scripting.
What if you implement the share as a script - something like @tracyanne mention or something like the script I linked earlier - something you can easily switch on and off as required?
EDIT:
For the sake of completeness - I have tested a setup similar to yours - for obvious reasons I cannot mimic your system.
I created a proof-of-concept samba server from scratch [1] using a full setup with users, permissions - everything needed to mimic an office like setup.
- Using dolpin on my workstation - I made a connection to the service
- Upon navigating the shared data folder - service requires credentials
- I provided admin credentials as setup for the service
- I navigated into the structure /data/public/
- I created two folders /data/public/folderA and /data/public/folderB
- I added the folders to the places pane using drag’n drop - folderA and folderB
- I dropped a file from my system /desktopfs-pkgs.txt onto folderA in the places pane
- I navigated into folderA and dragged the file desktopfs-pkgs.txt
- I dropped the file onto folderB in the places pane
During this simple proof-of-concept I have not been able to reproduce the issue described in your initial topic.
I know this comment won’t bring you further to a solution as I have no idea why are having the issue and not being able to reproduce - one is left to speculate …