Visual Studio gets source from oldest package not for referenced version

The ProGet server works for me. I'm working on Windows 2012R2 Server.
First I had the problem that the ProGet service was not recognized running when working with IIS installation (in dedicated Site with dedicated https binding). But the service was running without problems even when i ran the same command on console.
With the currently running embedded installation the service is shown as running.

With both variants I have the following problem:

When I update a package with source the new source won’t show up in Visual Studio.

Say I had the version 1.0.28 of a package with a bug. I fixed the bug in version 1.0.29 but Visual Studio loads the old source from the version 1.0.28.
Even when I remove the symbol caching folder the old source loads and shows up.
Both packages show up in the gallery with “Symbols and source files are available” and when I download the “Package with Symbols” from the gallery link the corrected source is in the downloaded nupkg.

Now when I remove the old package 1.0.28 from the gallery then the source cannot be found anymore from Visual Studio. If I clear out the symbol caching folder the new source is loaded. So why is it necessary to delete the package on gallery and remove the local symbols cache to get the new source? Shouldn't Visual Studio load automatically the source with the corresponding version of the package linked in project?

My Visual Studio Version is Premium 2013 Update 4.
Version 12.0.31101.00 Update 4
Microsoft .NET Framework
Version 4.5.50938

NuGet Package Manager 2.8.50926.663

ProGet is 3.3.11

Under “Symbols & Source” on the gallery is a link view which shows up where the pdb is located in the package. At the end of the line is a field named “Age”.
What does this field mean? Is there an indicator for such problems on indexing?
In my sample the version 1.0.28 shows an “Age” of 13 and the new version 1.0.29 shows the “Age” of 14.

I hope you have some suggestions for my problem.

Product: ProGet
Version: 3.3.11

Strange. If you open the Tools->Options->Debugging dialog in Visual Studio, is the "Require source files to exactly match the original version" item checked? If it is not checked, that may cause it to use an old source file in the debugger.

As far as I know, the PDB age is part of the symbol file's unique identifier - when Visual Studio asks for symbols, it makes a request to a URL with the PDB GUID and age. I think age normally gets incremented when a project is rebuilt in Visual Studio, though I don't know the rules about this for sure.

Since you get the correct symbols/source if you clear out the symbol directory, I'm guessing Visual Studio just isn't making a request to ProGet because it thinks it already has the correct files. The best thing to do in this case is to run Fiddler and capture a trace of both behaviors and see what's different. You can send us a copy of these to support at inedo.com if you want some help troubleshooting.