"Mixed Platforms" solution is created and selected when Solution Platforms are not default

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What steps will reproduce the problem?
1. Create solution that has A and B as solution platforms.
2. Use SolutionLoadManager to customize the selection of projects to load.
3. Reload the subset of solution projects.  Observe "Mixed Platforms" added and 
selected.

What is the expected output? What do you see instead?
Expect to have either A or B selected as an active Solution Platform.

What version of the product are you using? On what operating system?
0.2.1 and 0.2.2 on Windows 7 with VS2010 SP1

Please provide any additional information below.

Original issue reported on code.google.com by gcher...@gmail.com on 3 Aug 2011 at 8:04