I was having problems to get a macro with ReplInFiles running and it took me a while to find out why.

This does not work
ReplInFiles "C:\temp\ultra" "*.txt" "a" "b"

This does:
ReplInFiles "C:\temp\ultra\" "*.txt" "a" "b"

Well, I have several times written that the directory path must end with a backslash. So this is nothing new. See for example my GetListOfFiles.js script function which contains the code lines:
If you browse to a directory in Replace in Files dialog and select it, you will see in the dialog that the path of the selected directory ends with a backslash. It should be clear for everyone that when all directory paths in Replace in Files dialog end always with a backslash, that the macro command ReplInFiles requires also a backslash at end of the path.