Allow Contribution & Membership Price Sets to be used together

Whenever you attempt to add a Membership or Contribution Price Set to a Contribution Form that already has an existing Membership or Contribution Price Set, you receive this error:

"You cannot use a Membership Price Set when the Contribution Amounts section is enabled. Click the Memberships tab above, and select your Membership Price Set on that form. Membership Price Sets may include additional fields for non-membership options that require an additional fee (e.g. magazine subscription) or an additional voluntary contribution."

I'm not really certain what the reason for this is.

I currently have a site that has both enabled (from an older version) and I can no longer save the Contribution Form because of this conflict. I'm not sure when this was introduced or why, but I'm trying to figure out how to have both Memberships & Contributions on the same form. I understand that the error is saying that I should just use Membership Fields, but I'm not sure how you would specify different contributions on a Membership Price Set. Also, I need to be able to specify "Another Amount" which is currently impossible without http://issues.civicrm.org/jira/browse/CRM-14282