Rails hard codes the alternate link type in atom feed builder entries (see line 191 in https://github.com/rails/rails/blob/9ca58ba492fdd1729aa03ca8ec89be941a0f6d4e/actionpack/lib/action_view/helpers/atom_feed_helper.rb)
Could it be changed to an option for feed.entry, with a default of text/html? I can provide a patch if this is agreeable.
add type option to atom feed entry builder
I'm closing this issue, because @lest's PR fixed this problem.
If you have any problems, please comment to this issue.