I find Project level defines very useful. 
Unfortunately lately I am noticing some inconsistent behavior: sometimes the project builds as if the define was not there. 
Digging into it a bit I could see that the define showing in the Project Properties was not in the <PreprocessorDefinitions> section of the .vcxproj file. I don't know when the .vcxproj should be updated but if I close VS (confirming any proposed saves) and then reopen, the Project Properties match the .vcxproj file (= no define).

The most confusion part is that at some point multiple projects in the solution start showing the same defines in the Project Properties (after only making changes in one). This goes away after deleting the .vs folder under the solution. Seems related to the interaction between Visual Micro and Visual Studio around the display/updates of the  Project Properties panel. 
This happens in a solution with multiple (8) VM (Arduino)projects, some are also grouped in Solution Folders (I find that very convenient). 

I had to switch to dedicated headers just for holding defines I need to share across all compilation units in the projects. Using Project level defines would be much more convenient but is not reliable for me at this point.
This stared happening during the last few weeks. There have been VS updates and VM updates during this time and my solutions also got larger (more projects).

I wonder if anybody had encountered anything similar and hopefully found a fix.   

That's what I did, F4.  I only looked into the .vcxproj file after getting the behavior I described but did not attempt to change anything in the file. 

Right after deleting the .vs folder I can set defines (via Project Properties panel in VS), per each project, and moving between projects the defines are maintained as expected. 
However, at some point (?) when I set a define in one project, the Defines field shows the same content for all  the projects in the solution.
I'm describing what shows in the Project Properties before attempting to build anything yet.

I cannot pinpoint yet what triggers the behavior, I'll try the identify the steps to reproduce. I could take screen shots of the UI if that's useful.

It's not a terrible problem, can be easily worked around with dedicated header files but would be nice to have it.   

thanks