Oracle.DataAccess.dll not shown in explorer although it is installed in GAC

Question

Does anybody know why my Oracle.DataAccess.dll Version 4 assemblies are not shown in explorer view. It is installed in GAC and working without any problems. gacutil shows it as expected.

C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC>gacutil /l Oracle
Microsoft (R) .NET Global Assembly Cache Utility.  Version 4.0.30319.18020
Copyright (c) Microsoft Corporation.  All rights reserved.

The Global Assembly Cache contains the following assemblies:

Number of items = 0

C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC>gacutil /l Oracle.DataAccess
Microsoft (R) .NET Global Assembly Cache Utility.  Version 4.0.30319.18020
Copyright (c) Microsoft Corporation.  All rights reserved.

The Global Assembly Cache contains the following assemblies:
  Oracle.DataAccess, Version=2.112.1.0, Culture=neutral, PublicKeyToken=89b483f429c47342, processorArchitecture=AMD64
  Oracle.DataAccess, Version=2.112.4.0, Culture=neutral, PublicKeyToken=89b483f429c47342, processorArchitecture=AMD64
  Oracle.DataAccess, Version=2.112.1.0, Culture=neutral, PublicKeyToken=89b483f429c47342, processorArchitecture=x86
  Oracle.DataAccess, Version=2.112.2.0, Culture=neutral, PublicKeyToken=89b483f429c47342, processorArchitecture=x86
  Oracle.DataAccess, Version=2.112.4.0, Culture=neutral, PublicKeyToken=89b483f429c47342, processorArchitecture=x86
  Oracle.DataAccess, Version=4.112.2.0, Culture=neutral, PublicKeyToken=89b483f429c47342, processorArchitecture=AMD64
  Oracle.DataAccess, Version=4.112.4.0, Culture=neutral, PublicKeyToken=89b483f429c47342, processorArchitecture=AMD64
  Oracle.DataAccess, Version=4.112.4.0, Culture=neutral, PublicKeyToken=89b483f429c47342, processorArchitecture=x86

Number of items = 8

C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC>