Index: generic/schema.c
==================================================================
--- generic/schema.c
+++ generic/schema.c
@@ -121,21 +121,22 @@
     "ANY",
     "NAME",
     "CHOICE",
     "INTERLEAVE",
     "PATTERN",
-    "TEXT"
+    "TEXT",
     "VIRTUAL",
     "KEYSPACE_START",
     "KEYSPACE_END"
 };
 static char *Schema_Quant_Type2str[] = {
     "ONE",
     "OPT",
     "REP",
     "PLUS",
-    "NM"
+    "NM",
+    "ERROR"
 };
 #endif
 
 
 #ifndef TCL_THREADS
@@ -1067,16 +1068,11 @@
                 }
                 break;
 
             case SCHEMA_CTYPE_VIRTUAL:
                 if (evalVirtual (interp, sdata, ac)) {
-                    /* Virtual contraints are always quant ONE, so
-                     * that the virtual constraints are called while
-                     * looking if an element can end. Therefor we use
-                     * here the already present mayskip mechanism to
-                     * try further, after calling the tcl script. */
-                    mayskip = 1;
+                    hm = 1;
                     break;
                 }
                 else return 0;
 
             case SCHEMA_CTYPE_INTERLEAVE:
@@ -1086,10 +1082,11 @@
                 if (rc == 1) {
                     updateStack (se, cp, ac);
                     return 1;
                 }
                 popStack (sdata);
+                if (rc == -1) mayskip = 1;
                 break;
 
             case SCHEMA_CTYPE_KEYSPACE_END:
                 candidate->keySpace->active--;
                 if (!candidate->keySpace->active) {
@@ -4204,11 +4201,11 @@
     for (i = 1; i < objc; i++) {
         pattern->content[i-1] = (SchemaCP *) objv[i];
         Tcl_IncrRefCount (objv[i]);
     }
     pattern->nc = objc;
-    addToContent (sdata, pattern, SCHEMA_CQUANT_OPT, 0, 0);
+    addToContent (sdata, pattern, SCHEMA_CQUANT_ONE, 0, 0);
     return TCL_OK;
 }
 
 static int
 domuniquePatternObjCmd (

Index: tests/schema.test
==================================================================
--- tests/schema.test
+++ tests/schema.test
@@ -4692,10 +4692,38 @@
         lappend result [s validate $xml errMsg]
     }
     s delete
     set result
 } {1 1 0}
+
+test schema-16.17 {interleave with all content cp optional} {
+    tdom::schema s
+    s defelement doc {
+        interleave {
+            element a ?
+            element b ?
+            element c ?
+        }
+        element d
+    }
+    set result [list]
+    foreach xml {
+        <doc/>
+        <doc><a/><d/></doc>
+        <doc><b/><d/></doc>
+        <doc><c/><d/></doc>
+        <doc><a/><c/><d/></doc>
+        <doc><b/><c/><d/></doc>
+        <doc><c/><a/><d/></doc>
+        <doc><c/><a/><b/><d/></doc>
+        <doc><c/><a/><b/></doc>
+    } {
+        lappend result [s validate $xml]
+    }
+    s delete
+    set result
+} {0 1 1 1 1 1 1 1 0}
 
 test schema-17.1 {info} {
     tdom::schema s
     s define {
         foreach e {a b1 b11 b2 c} {
@@ -4920,11 +4948,11 @@
         s event start doc
         lappend result {*}[s info frontexpected]
         s delete
     }
     set result
-} {a b c a b c a b c d}
+} {a b c a b c d a b c d}
 
 proc schema-18 {args} {
     lappend ::result {*}$args
 }
 test schema-18.1 {reportcmd} {