New StartArguments aren't always applied when launching an app

## Visual Studio Version
17.1.4

## Summary
Changes to the `StartArguments` element of a .csproj file are not always applied when the app is launched.

## Steps to Reproduce
1. Change the `StartArguments` in a .csproj file
2. Without saving the project file, launch the app for debugging.

## Expected Behavior
The .csproj file is saved and the new arguments are used in the debugging session.

## Actual Behavior
The .csproj file is saved, but the old arguments are used. A subsequent launch will use the new arguments.

I can also get this to reproduce by manually saving the .csproj and quickly pressing F5 to debug, but there seems to be a timing element to this. Leave a long enough gap between the save and launch, and the bug won't reproduce.