Reproduction steps:

1. Open Unity and create a New Project
2. Create a C# Script and open it with Visual Studio (Do any changes just to save the script)
3. Close Unity and VS
4. Open project folder
5. Open "ProjectName.sln" file with a text editor
6. Replace TextA with TextB
7. Open the project
8. Step 5

Expected Result: The stored custom settings stay the same after restart
Actual Result: The store custom settings are removed and the file defaults itself

Won't Fix: Bug is on Visual Studio side. It has been reported to their team and awaits a fix.

Reproduced with: 2018.1.0a1, 2017.3.0b5, 2017.2.0f3, 2017.1.2p1, 5.6.4p1, 5.6.1f1
Did not reproduce on: 5.6.0p4(Can't use VS for some reason), 5.6.0p3, 5.6.0p1, 5.6.0f3, 5.6.0f1, 5.6.0b1, 5.6.0a5, 5.5.5p1

Note:
Only affects Visual Studio(But not Visual Studio Code)

TextA:
"GlobalSection(SolutionPropertoies) = preSolution
HideSolutionNode = FALSE
EndGlobalSection"

TextB:
"GlobalSection(SolutionProperties) = preSolution
HideSolutionNode = FALSE
EndGlobalSection
GlobalSection(MonoDevelopProperties) = preSolution
Policies = $0
$0.TextStylePolicy = $1
$1.scope = text/x-csharp
$1.FileWidth = 100
$1.TabsToSpaces = True
$1.EolMarker = Unix
$0.CSharpFormattingPolicy = $2
$2.NewLinesForBracesInProperties = False
$2.NewLinesForBracesInAccessors = False
$2.NewLinesForBracesInAnonymousMethods = False
$2.NewLinesForBracesInControlBlocks = False
$2.NewLinesForBracesInAnonymousTypes = False
$2.NewLinesForBracesInObjectCollectionArrayInitializers = False
$2.NewLinesForBracesInLambdaExpressionBody = False
$2.NewLineForElse = False
$2.NewLineForCatch = False
$2.NewLineForFinally = False
$2.NewLineForMembersInObjectInit = False
$2.NewLineForMembersInAnonymousTypes = False
$2.NewLineForClausesInQuery = False
$2.scope = text/x-csharp
$0.TextStylePolicy = $3
$3.FileWidth = 100
$3.TabsToSpaces = True
$3.EolMarker = Unix
$3.scope = text/plain
$0.DotNetNamingPolicy = $4
$0.TextStylePolicy = $5
$5.FileWidth = 100
$5.TabsToSpaces = True
$5.EolMarker = Unix
$5.scope = application/xml
$0.XmlFormattingPolicy = $6
$6.scope = application/xml
$0.StandardHeader = $7
EndGlobalSection"