This came up internally at Microsoft. One of our teams makes heavy use of creating symlinks and using them in the build. This causes problems when the symlink is newly created, but its target is old. In that case, we unnecessarily choose to rebuild.

From that internal thread:

You must examine the timestamp of the actual file, not the symlink file. (For managed code, this means using File.GetLastWriteTime instead of FileInfo.GetLastWriteTime. For native code, it means using GetFileTime instead of GetFileAttributesEx.)

IsUpToDate does the check through NativeMethods.GetLastWriteTimeUtc, which does indeed call GetFileAttributesEx.