Time zones being re-written when files are processed from refernced files

I'm having a problem where photos with time zones set are being re-written automatically to whatever time zone my mac is currently set at when Aperture processes them for viewing regardless of the time zone they were set to. This happens as the photos load for viewing (i.e. not on the browser thumbnail view). It does this one at a time and eats up processing time. This seems to only happen (I think) for referenced files stored on my external drive and not those stored in the Aperture library. If I re-set the photos back to the proper time zones using Batch Change, it still happens next time it has to load the photo into memory, again "processing" and again the time zone reset to whatever time zone I'm now in.

Here's the exact situation:
- I've imported several photosets from a Canon 50D. The camera was set to the time zone of the country in question. Let's use India at GMT +5:30 as an example.
- When I import the photos, I also use the time zone presets, setting both the Camera Time and the Actual Time to GMT +5:30.
- I'm importing the photos as referenced files, storing them on an external hard drive.
- So when I first view the photos, the time and date show correct. Again using a real example IMG_0001 shows the date 6/10/10 1:43:31 PM GMT +05:30.
- Now I close Aperture and re-open.
- I open the folder and view the photo. The "loading" message appears at the time and the "processing" message appears on the bottom. (and during this unnecessary processing, it is very slow flipping to the next photo, a serious annoyance in browsing).
- After processing, the photo IMG_0001 now shows the date as 6/10/10 1:43:31 PM GMT +03:00 (the time zone I'm currently in and the one my Mac is currently set to)
- If I close it again and re-set my Mac to say I'm in London at GMT, and re-open, the photo is re-set instead to GMT.
- I can re-set all the dates to the proper time zone using the Batch Change where I again set both the Camera Time and Actual Time to the correct time zone. But when the photo re-loads, it again re-processes and goes back to the date of the Mac. So changes don't seem to stick.
- This appears to happen only to files that are referenced and stored on my external drive, not those stored in the Aperture library.

Has anyone had this problem? Is it a bug or some hidden setting I'm missing? Is there some way to tell Aperture "don't change the dates, ever, unless I do it via batch change"? The problem turns into a major inconvenience in reviewing and editing photos with it taking the extra processing time every photo and messing around the order.