I recently changed from 2007 to 2010. I have a DB with a split form. If I change the column widths in the table part of the split, the changes do not save. In a newly created database with dummy data and fresh split form, the changes do save.
I was able to solve this while posting, but I will maintain the post for posterity. I hid and unhid columns and things came 'unstuck' eventually. They did not start working with the first hide/save, and I may have started to delete a column but not finished. I'm not really sure how it started working again.