CSV Import Wizard does not work with custom fields anymore

The CSV Import Wizard does not work anymore with configuration files containing custome fields.
Every existing custom field is mapped to "None".

In the list of unmapped custom fields the name of the unmapped column appears wrong:

Unmapped CSV header
ActionexistingCustomField

(see also attachment).
There should be a blank or another Separator between "Action" (the column name)
and "existingCustomField" (the type of field).
Probably due to this missing separator the wizard cannot match the column name!

Using the same import configuration file just for doing an import shows no problem.
The data is imported correctly. Only the wizard does not work anymore, so if you have
to modify the import configuration you have to do this by editing the cfg file manually.