.

wcfs/internal/xbtree/δbtail.go

@@ -316,7 +316,7 @@ func (δTtail *ΔTtail) rebuild(root zodb.Oid, δZtail *zodb.ΔTail, db *zodb.DB
 	vδZ := δZtail.Data()
 	for {
 		δtkeycov := &RangedKeySet{}     // all keys coming into tracking set during this lo..hi scan
-		trackNewCur := trackNew.Clone()
+		trackNewCur := trackNew.Clone() // trackNew adjusted when going to i<- entry
 		for i := len(vδZ)-1; i>=0; i-- {
 			δZ := vδZ[i]
 

wcfs/internal/xbtree/δbtail_test.go

@@ -1066,10 +1066,11 @@ func xverifyΔBTail_rebuild(t *testing.T, db *zodb.DB, treeRoot zodb.Oid, t0, t1
 							xverifyΔBTail_rebuild_TR(t, db, δbtail_, t2, treeRoot, xat,
 								// after Track(keys2)
 								keys2,
-//								/*trackSet*/ t2.xkv.trackSet(keys1_0.Union(keys1_2)),
 								/*trackSet*/ t2.xkv.trackSet(keys1_2),
-								// FIXME vvv trackNew should not cover ranges that are already in trackSet
-								/*trackNew*/ t2.xkv.trackSet(keys2),
+								/*trackNew*/ t2.xkv.trackSet(keys2).Difference(
+									// trackNew should not cover ranges that are
+									// already in trackSet
+									t2.xkv.trackSet(keys1_2)),
 
 								// after rebuild
 								/* trackSet=*/ t2.xkv.trackSet(keys12R),