SET command in MS-DOS Batch Functions

Just seems like it does not work.

Trivial examples:

Notepad "T:\Temp\aaaaaaaaaaaaaaaa\zmorojewo.epub"

this works.

SET aaa=bbb Notepad "T:\Temp\aaaaaaaaaaaaaaaa\zmorojewo.epub"
this does not work; no effect at all.

Both are MS-DOS Batch Functions. I've tried them in menu and in context menu.
Second example in .cmd file is working as expected: it opens CLI window and outputs:

[code]T:\Temp\aaaaaaaaaaaaaaaa>SET aaa=bbb

T:\Temp\aaaaaaaaaaaaaaaa>Notepad "T:\Temp\aaaaaaaaaaaaaaaa\zmorojewo.epub"[/code]
and opens Notepad with "zmorojewo.epub".

Is this bug, or I'm doing something wrong?

Directory Opus Pro 10.5.2.5 (4997) x64
OS 6.2 (B:9200 P:2 T:1) SP 0.0

Look up @externalonly in the manual:

gpsoft.com.au/help/opus10/defaul ... erence.htm

Thanks.
I was under false impression that in MS-DOS Batch Functions only DOpus external control codes are allowed, but not internal commands.