Problem with multiple portable versions in Windows 7

[Sybell Lirwaco]

I have a problem with multiple portable versions in a Windows 7.
I use one notepad++ for general purposes. Another only as an SFTP client editor.
Currently, because of the UTF-8 code issue, version 7.5.1.

General:
C:\Users\xxx\Portable\npp.7.5.1.bin.x64\notepad++. exe
Settings:
no multiInst.
.txt file association to npp.7.5.1.bin.x64\notepad++. exe
(checked in the registry)

SFTP Client Editor:
C:\Users\xxx\Portable\npp.7.5.1.bin.minimalist.x64\notepad++. exe
Settings:
notepad++ Preferences: Multiinst
SFTP client linking: npp.7.5.1.bin.minimalist.x64/notepad++. exe -multiInst

If a file is opened via SFTP client via preferences linked npp.7.5.1.bin.minimalist.x64 and then opened a txt file in Windows Explorer, then the txt file is opened in the opened npp.7.5.1.bin.minimalist.x64 by the SFTP client, even if a npp.7.5.1.bin.x64 window is already open. A txt file opened from Explorer always opens in the last active notepad++ window. How is this possible and how can I prevent it?