How to avoid filtered photos being automatically resized?

When I take pictures with the main camera using any of the built-in Camera filters, they appear to be saved in a scaled-down size. Eg for a non-filtered picture in full size, the resolution is 3264x2448 pixels, while a photo taken with a filter (or with a filter applied after shooting it) gets scaled down to 2048x1536 pixels. I noticed this after sharing some images via email in 'full size', only to notice that only non-filtered images would actually be shared in full size.

The curious thing is, I use Flickr's auto upload feature, and all photos are uploaded to my Flickr account in full resolution, with the correct filters applied. This is the only way I know of accessing (hence being able to save/share) my filtered pictures in full resolution.

Any idea on how to be able to access my filtered photos in full size, without using the Flickr trick?

Thanks