I have an app that used XOR mode with various graphics primitives and I noticed that filled ellipses did not show correctly when XOR mode was set.  I took a quick glance at the xwin.c file to see if the fix would be obvious and it seems to be.  The filled ellipse drawing code was handled differently than the other drawing methods and when I switched it to be consistent the problem was fixed.  I admit to knowing nothing about the code base, but hopefully this will point somebody in the right direction for a 'real' fix if it's not right.  NOTE: my patch is against the 1.4.1 source drop.

--- xwin.c
+++ xwin.c
@@ -137,10 +137,9 @@
                                XDrawArc(g_display, g_backstore, g_gc, x, y, cx, cy, 0, 360*64); \
                        break; \
                case 1: /* Filled */ \
-                       XFillArc(g_display, g_ownbackstore ? g_backstore : g_wnd, g_gc, x, y, \
-                                cx, cy, 0, 360*64); \
+                       XFillArc(g_display, g_wnd, g_gc, x, y, cx, cy, 0, 360*64); \
                        if (g_ownbackstore) \
-                               XCopyArea(g_display, g_backstore, g_wnd, g_gc, x, y, cx, cy, x, y); \
+                               XFillArc(g_display, g_backstore, g_gc, x, y, cx, cy, 0, 360*64); \
                        break; \
        } \
 }