Hi Jakub,
Thanks for the fast response.
Actually I noticed it happens even when not debugging, sorry if I didn't make that clear in my edit.
It's a purely PHP project, no C#.
I looked at general Visual Studio posts about this on the internet and saw the solution as just to 'exclude from project', which works.
So, it's not a bug or any fault of your (fantastic!) software. Perhaps it's worth thinking about if any other users are attributing any slow downs to your plugin. Or having an article about it on your help forum. Otherwise, I guess there's nothing needed to be done.
To replicate, I used the 'ProcessMon' type tools from SysInternals and I saw the msbuild running each time the website was refreshed and session file was created/updated.
Cheers,
John