Watch out For Withholding on Sales of US Partnership Interests by Nonresidents
Tax Reform created a 10% withholding tax applicable to a foreign person's sale, exchange, or other disposition of a U.S. partnership interest. Now, gain or loss resulting from the sale or an exchange of a foreign partner’s interest in a U.S. partnerships is considered U.S. effectively connected income subject to withholding.
Strangely enough, the burden of collecting the withholding tax is imposed on the U.S. person acquiring the partnership interest. So watch out if you are purchasing a partnership interest from a foreign person. If no withholding was done, you will be liable for the tax you should have withheld!