CS5- Custom Links to EPS Files Don't Work?

Question

I am building a plugin that allows a user to place graphic assets from our own external asset management system into their InDesign document.  These assets need to maintain a "custom link" to the external assets.
Everything was working great for simple raster image formats (like JPEG) but the custom link information seems to get lost for EPS files.
After doing some deep debugging I decided to try building one of the sample plugins that ship with CS5 - 'customdatalink' and the accompanying 'customdatalinkui'.  This sample does a similar type of thing with CSV files that reference external assets.
To make a long story short, the sample plugin exhibits the exact same behavior.  If you edit one of the sample csv files to point to an EPS image and place that in a document, you'll see that the Link URI is replaced with a file:// style path instead of the custom csv:// URI.  It works as expected for JPEG files.
Surely this is not expected behavior.  Am I missing something obious here or is this a simple (but pretty major for my plugin) bug?
Thanks in advance for any assistance.
p.s. this behavior is identical on both Mac and Windows.

Answer 1

Here's a bit more detail. Again the idea is to return an IPMStream that doesn't include a IID_IFILESTREAMDATA. So I make a proxy IPMStream that just forwards requests to a real IPMStream.
I've abbreviated a bit here for space reasons.
So I make my own IPMStream object adding the class to my .fr file:
class FileProxyWriteStream : public CPMUnknown<IPMStream>
public:
               FileProxyWriteStream(IPMUnknown* boss);
          virtual     ~FileProxyWriteStream();
          void SetRealStream(IPMStream *, AeInDesignGeo *);
          virtual uchar XferByte(uchar& chr) { return mRealStream->XferByte(chr); }
... all IPMStream methods
Create my proxy stream:
proxyStream = ::CreateObject2<IPMStream>(kFileProxyWriteStreamBoss, IID_IPMSTREAM);
And I create a IPMStream:
InterfacePtr<IPMStream>          realStream(StreamUtil::CreateFileStreamReadLazy(file, kOpenIn));
Tell my proxyStream about the realStream
proxyStream->SetRealStream(proxyStream);
and CreateResourceReadStream returns my proxyStream
Hope this helps
-doug