Thanks for the reply, and the link. I hadn't picked up on that error - I usually right click in search results and open from there, rather than using the thumbnails. When you work that way you can still add to the current session. I just tried opening via the thumbnails and was able to replicate that issue; I also tried it in chrome and as you say it creates a separate Creo View session.
I would quite like to use Chrome as default for Windchill, but in the past I have had issues with it not working well with java related activities so I tend to stick with IE.
I guess I won't be satisfied until I get the "Open Multiple Drawings in Creo View" button, I should probably create a product idea for it.
Thanks,
Dave