it seems that for any external editor, the "!.!" part of the command line is limited to 100 characters, so it is possible to open a file called "1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890", but a file called "12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901" (i.e. with 1 more character) will not be opened because the editor receives the filename "1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890". No joke, I actually have to deal with such long filenames :-)
The problem doesn't occur in the internal editor.