IIRC the maximum command line length in MS-DOS is 127 characters -- this could be the limit you're running into with the RUN command (and possibly less, especially if RUN issues something along the lines of "COMMAND.COM /C cmd").
http://support.microsoft.com/kb/69563
> Each batch file line does have a limit, however. Any batch file line exceeding 127 bytes is truncated at 127 bytes before it is processed.
(note: I haven't checked if this restriction still applies in anything beyond MS-DOS. I recall in MS-DOS you couldn't enter command longer than a certain length. Win95/98 seemed to allow longer line length)

I remember back in the "old days" in using DOS where I had to use input response files with some compilers and linkers because the required command line could easily exceed maximum line length (especially if you had to list full paths to libraries and/or required passing a lot of command-line options). Of course use of input response file (not I/O redirection, but a text file that specifies parameter/option list -- often they took format of pre-pending "@" in front of filename that contains this information) requires that the software you're using knows how to handle them.