Created attachment 165129 [details]
Error dialog

SUMMARY
ExFAT doesn't allow file names with characters like question marks, colons, etc. When copying a file folder that has such a character in its name, Dolphin is smart enough to suggest renaming it on the fly. However, the contents of the folder then fail to be copied to the renamed location.

STEPS TO REPRODUCE
You need a disk formatted with a proper filesystem like ext4 and a flashdrive formatted with exfat.
1. Create a folder in your ext4 disk with a name that contains question marks eg: "hello??". Create one file inside the folder.
2. Copy the folder to the exFAT disk. Dolphin suggests to rename it to replace the question marks, which are not valid in exfat, in the previous example to "hello__".

OBSERVED RESULT
3. Dolphin fails to copy the contents of the directory, with the attached error. (BONUS BUG: the filename is cropped even if I resize the window, so I can't never fully read the file path).

EXPECTED RESULT
Once the folder is renamed, the contents should be copied successfully from the unrenamed to the renamed.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: master
KDE Plasma Version: master
KDE Frameworks Version: master 
Qt Version: master