java.lang.Error: Structure.getFieldOrder() return names don't match declared field names (but they do)

I'm trying to obfuscate some code, and one of my methods in the main class references this Shell32X.java class. The method in the main class (not shown here) is supposed to call another program that has an admin manifest, so that the UAC prompt will appear. When I obfuscate the main jar I get an error pointing to this referenced class (below):
java.lang.Error: Structure.getFieldOrder() on class MyMainClass returns names ([cbSize, dwHotKey, fMask, hInstApp, hKeyClass, hMonitor, hProcess, hwnd, lpClass, lpDirectory, lpFile, lpIDList, lpParameters, lpVerb, nShow]) which don't match declared field names
But as fas as I can tell, they do match. So what is the problem?

import java.util.Arrays;
import java.util.List;
import com.sun.jna.Native;
import com.sun.jna.Pointer;
import com.sun.jna.Structure;
import com.sun.jna.WString;
import com.sun.jna.platform.win32.Shell32;
import com.sun.jna.platform.win32.WinDef.HINSTANCE;
import com.sun.jna.platform.win32.WinDef.HWND;
import com.sun.jna.platform.win32.WinNT.HANDLE;
import com.sun.jna.platform.win32.WinReg.HKEY;
import com.sun.jna.win32.W32APIOptions;

public interface Shell32X extends Shell32
{
    Shell32X INSTANCE = (Shell32X)Native.loadLibrary("shell32", Shell32X.class, W32APIOptions.UNICODE_OPTIONS);

    int SW_HIDE = 0;
    int SW_MAXIMIZE = 3;
    int SW_MINIMIZE = 6;
    int SW_RESTORE = 9;
    int SW_SHOW = 5;
    int SW_SHOWDEFAULT = 10;
    int SW_SHOWMAXIMIZED = 3;
    int SW_SHOWMINIMIZED = 2;
    int SW_SHOWMINNOACTIVE = 7;
    int SW_SHOWNA = 8;
    int SW_SHOWNOACTIVATE = 4;
    int SW_SHOWNORMAL = 1;

    /** File not found. */
    int SE_ERR_FNF = 2;

    /** Path not found. */
    int SE_ERR_PNF = 3;

    /** Access denied. */
    int SE_ERR_ACCESSDENIED = 5;

    /** Out of memory. */
    int SE_ERR_OOM = 8;

    /** DLL not found. */
    int SE_ERR_DLLNOTFOUND = 32;

    /** Cannot share an open file. */
    int SE_ERR_SHARE = 26;



    int SEE_MASK_NOCLOSEPROCESS = 0x00000040;


    int ShellExecute(int i, String lpVerb, String lpFile, String lpParameters, String lpDirectory, int nShow);
    boolean ShellExecuteEx(SHELLEXECUTEINFO lpExecInfo);



    public static class SHELLEXECUTEINFO extends Structure
    {
        /*
         * DWORD     cbSize;
         * ULONG     fMask;
         * HWND      hwnd;
         * LPCTSTR   lpVerb;
         * LPCTSTR   lpFile;
         * LPCTSTR   lpParameters;
         * LPCTSTR   lpDirectory;
         * int       nShow;
         * HINSTANCE hInstApp;
         * LPVOID    lpIDList;
         * LPCTSTR   lpClass;
         * HKEY      hkeyClass;
         * DWORD     dwHotKey;
         * union {
         *  HANDLE hIcon;
         *  HANDLE hMonitor;
         * } DUMMYUNIONNAME;
         * HANDLE    hProcess;
         */

        public int cbSize = size();
        public int fMask;
        public HWND hwnd;
        public WString lpVerb;
        public WString lpFile;
        public WString lpParameters;
        public WString lpDirectory;
        public int nShow;
        public HINSTANCE hInstApp;
        public Pointer lpIDList;
        public WString lpClass;
        public HKEY hKeyClass;
        public int dwHotKey;

        /*
         * Actually:
         * union {
         *  HANDLE hIcon;
         *  HANDLE hMonitor;
         * } DUMMYUNIONNAME;
         */
        public HANDLE hMonitor;
        public HANDLE hProcess;

        @SuppressWarnings({ "unchecked", "rawtypes" })
        protected List getFieldOrder() {
            return Arrays.asList(new String[] {
                "cbSize", 
                "fMask", 
                "hwnd", 
                "lpVerb", 
                "lpFile", 
                "lpParameters",
                "lpDirectory", 
                "nShow", 
                "hInstApp", 
                "lpIDList", 
                "lpClass",
                "hKeyClass", 
                "dwHotKey", 
                "hMonitor", 
                "hProcess"
            });
        }
    }

}