I also have a problem with Google Drive offline access, don't now if it's the same as you.
With Google Drive online, no problem, it is downloading the file, and then opening the corresponding external app.
But if I set the file on offline acces, then the behaviour is depending on the file:
- with pdf file, no problem, the file is downloaded into Google Drive data folder on the SD card, with a copy in the data partition and opened with Adobe reader.
- with xls file, the file is only downloaded into Google Drive data folder on the SD card, and then Docs to Go isn't able to open it (looking for it on the data partition).