Race condition/path mix-up when batch executing custom commands with similar filenames

When selecting multiple files with similar prefixes (e.g., inv_conf.html and investor_fin.html) to run a custom diff command using ! and !^!, WinSCP's background variable dispatch seems to suffer from a race condition or path mix-up. The external script often receives swapped or incorrect file paths.
Steps to reproduce:
Set up a local custom command using PowerShell to launch WinMerge with !^! and !.
Select multiple files with similar names in both panels (equal quantity).
Trigger the custom command.
Expected result: Each file pair should be mapped correctly.
Actual result: Paths are cross-contaminated (wrong files compared).

First, please note that the files are paired simply by their order, not by their name. If that does not explain the mix-up, please post some screenshots documenting it.

Thank you for the clarification regarding ordinal sequence pairing.

However, the issue occurs specifically within the "Compare Directories" (Shift+F2) checklist window:

1. I perform a directory comparison (Shift+F2) to filter the modified files.
   
2. The list visually shows aligned, matching filenames on both local and remote panels.
   
3. When I select multiple files from this comparison list and execute the custom command, the parameters ! and !^! still dispatch incorrect pairings (a file gets compared with a different file in the batch).
   

It seems that the custom command dispatch mechanism loses track of the 1-to-1 ordinal mapping when triggered from the directory comparison checklist view.

If you use "Compare directories", WinSCP will highlight/select the mismatched files. Not any pairs.

Instead, use Synchronize command and execute your custom command from the Synchronization checklist window:
https://winscp.net/eng/docs/ui_synchronize_checklist