Some types dont show the inheritance modifiers in their members or some members.
The extrange thing is that other types in the same assembly show them.
If we look into mscorlib.dll

You can find that System.Object class shows virtual modifiers in its virtual members and also Int32 struct shows ToString method as override.
I found the problem looking at System.IO.FileSystemInfo class. The class appears marked as abstract but its abstract members dont have modifiers when decompiled. If we look at its inheriting classes (System.IO.FileInfo and System.IO.DirectoryInfo) they also dont show the override modifier when implementing the abstract properties and methods of FileSystemInfo.

This sounds like a good thing to fix.
The version I'm using is   2012.2.709.1

Hello,

 You are completely right. This is a case we haven't covered. Thanks a bunch for letting us know about it. We'll definitely fix that. Please, stay tuned.

Greetings,
Tsviatko Yovtchev
the Telerik team