Media Size changes don't take

I changed the Media Size setting for “Large” images from 480 X 480 to 850 X 850. I know this won’t go back and change old images unless I regenerate thumbnails. Anyway, I am uploading new images that are 1500 X 1500. WordPress creates an 850 X 850 file, but when I go to Add Media to a post, it still says 480 X 480 in the Attachment Display Settings. If I go ahead an put in the Large image, it refers to the 850 X 850 file, but gives it a width and height of 480. Any idea why? How can I fix it?

Theme is Inkblot, site is shinglestylehomeplans.com/gin-lane-southampton/

<img src="http://shinglestylehomeplans.com/wp-content/uploads/2014/07/Z-1-first-floor-plan-850x850.jpg" alt="1st Floor Plan - Gin Lane - Southampton" width="480" height="480" class="alignright size-large wp-image-171" />