To reproduce:
Have a directory structure like D:\MRT\test one\test two\test three (each containing a space)
and directories sorted alphabetically (Options > Display > Sorting directories set to "Always by name")
- cd to D:\, mark the base test dir (D:\MRT)
- press Alt+F7 (cm_SearchFor) (this option is activated by TC: [X] Only search in selected directories/files)
- enter " " (a space) in "Search for" field
- press "Start search" button => all three test folders are found
- press "Feed to listbox" button
- mark all found entries and press Ctrl+M (starts Multi Rename Tool)
- enter in Search for: " " (space, without quotation marks)
- enter in Replace with: "_" (underscore, without quotation marks)
- press Start
On a second run it would rename the second level and show the error for the third level, and so on.
For larger directory structures a lot of runs would be needed to finish the task.
If MRT would do renaming of child folders before their parents it would not fail on sub-directories.
Manual workaround (this way it works):
Turn off before starting MRT: Options > Display > Sorting directories is set to "Always by name",
then in MRT sort by name in negative order before pressing Start.
Turn on again after leaving MRT: Options > Display > Sorting directories is set to "Always by name",
Suggestion:
(Internally) always sort directories in MRT by name/path in negative order - this should avoid subdir conflicts regardless of displayed sorting.