Worth noting that official WinSCP is portable too, so there's probably no need to use WinSCP Portable.
https://winscp.net/eng/docs/portable

Thanks for your quick reply! You are right! I installed version 5.1.4 now and couldn't reproduce the bug there. It only appears in the portable version I got from https://portableapps.com/apps/internet/winscp_portable
I wasn't aware that this might not be the original version but a fork. Thanks for clearing this out! I'll report the bug to the forum there! All best to you! Many thanks for your good work!

I was not able to reproduce the problem.
Are you using offical WinSCP with INI file or some "portable" fork of WinSCP?
Can you provide me step by step instructions how to reprodcue the problem?

I use WinSCP portable in version 5.1.3 and need integration of PuTTY. In the menu/settings: Options/Preferences/Integration/Applications there is a default value in "PuTTY path". When I change this default path to the real path where my PuTTY is located and then click "OK" to save this setting, then the connection works as long as this WinSCP session is lasting. But after closing and restarting WinSCP portable, the setting of the PuTTy path is back to the default value. The same happens if I click the "Reset" button in the PuTTY path setting: After restarting WinSCP portable the path is back to the default value. Any other settings are stored correctly, so it does not seem to be a case of write protection of my .ini file.