diff --git a/RDFSharp.Test/Model/RDFGraphTest.cs b/RDFSharp.Test/Model/RDFGraphTest.cs
index dc88bc05..98e4e2cf 100644
--- a/RDFSharp.Test/Model/RDFGraphTest.cs
+++ b/RDFSharp.Test/Model/RDFGraphTest.cs
@@ -255,6 +255,31 @@ public void ShouldAddTripleAsImport()
             Assert.IsTrue(graph.Count(t => t.TripleMetadata == RDFModelEnums.RDFTripleMetadata.IsImport) == 1);
         }
 
+        [TestMethod]
+        public void ShouldAddTriplesMixingMetadata()
+        {
+            RDFGraph graph = new RDFGraph();
+            RDFTriple triple1 = new RDFTriple(new RDFResource("http://subj/"), new RDFResource("http://pred/"), new RDFPlainLiteral("lit","en-US"));
+            RDFTriple triple2 = new RDFTriple(new RDFResource("http://subj/"), new RDFResource("http://pred/"), new RDFResource("http://obj/"))
+                                    .SetMetadata(RDFModelEnums.RDFTripleMetadata.IsInference);
+            RDFTriple triple3 = new RDFTriple(new RDFResource("http://subj/"), new RDFResource("http://pred/"), new RDFPlainLiteral("lit"))
+                                    .SetMetadata(RDFModelEnums.RDFTripleMetadata.IsImport);
+            graph.AddTriple(triple1);
+            graph.AddTriple(triple2);
+            graph.AddTriple(triple3);
+
+            Assert.IsTrue(graph.TriplesCount == 3);
+            Assert.IsTrue(graph.IndexedTriples.ContainsKey(triple1.TripleID));
+            Assert.IsTrue(graph.IndexedTriples[triple1.TripleID].TripleMetadata is null);
+            Assert.IsTrue(graph.IndexedTriples.ContainsKey(triple2.TripleID));
+            Assert.IsTrue(graph.IndexedTriples[triple2.TripleID].TripleMetadata == RDFModelEnums.RDFTripleMetadata.IsInference);
+            Assert.IsTrue(graph.IndexedTriples.ContainsKey(triple3.TripleID));
+            Assert.IsTrue(graph.IndexedTriples[triple3.TripleID].TripleMetadata == RDFModelEnums.RDFTripleMetadata.IsImport);
+            Assert.IsTrue(graph.Count(t => t.TripleMetadata is null) == 1);
+            Assert.IsTrue(graph.Count(t => t.TripleMetadata == RDFModelEnums.RDFTripleMetadata.IsInference) == 1);
+            Assert.IsTrue(graph.Count(t => t.TripleMetadata == RDFModelEnums.RDFTripleMetadata.IsImport) == 1);
+        }
+
         [TestMethod]
         public void ShouldNotAddDuplicateTriples()
         {
diff --git a/RDFSharp.Test/Model/RDFTripleTest.cs b/RDFSharp.Test/Model/RDFTripleTest.cs
index 046651fa..456e19af 100644
--- a/RDFSharp.Test/Model/RDFTripleTest.cs
+++ b/RDFSharp.Test/Model/RDFTripleTest.cs
@@ -52,6 +52,10 @@ public void ShouldCreateSPOTriple(string s, string p, string o)
             Assert.IsNull(triple.TripleMetadata);
             triple.SetMetadata(RDFModelEnums.RDFTripleMetadata.IsInference);
             Assert.IsTrue(triple.TripleMetadata == RDFModelEnums.RDFTripleMetadata.IsInference);
+            triple.SetMetadata(RDFModelEnums.RDFTripleMetadata.IsImport);
+            Assert.IsTrue(triple.TripleMetadata == RDFModelEnums.RDFTripleMetadata.IsImport);
+            triple.SetMetadata(null);
+            Assert.IsTrue(triple.TripleMetadata is null);
         }
 
         [DataTestMethod]
diff --git a/RDFSharp.Test/RDFSharp.Test.csproj b/RDFSharp.Test/RDFSharp.Test.csproj
index 55aa9270..ade287a5 100644
--- a/RDFSharp.Test/RDFSharp.Test.csproj
+++ b/RDFSharp.Test/RDFSharp.Test.csproj
@@ -3,7 +3,7 @@
 		<AssemblyTitle>RDFSharp.Test</AssemblyTitle>
 		<AssemblyName>RDFSharp.Test</AssemblyName>
 		<AssemblyVersion>$(Version)</AssemblyVersion>
-		<Version>3.8.1</Version>
+		<Version>3.9.0</Version>
 		<Authors>Marco De Salvo</Authors>
 		<Copyright>Marco De Salvo</Copyright>
 		<TargetFramework>net6.0</TargetFramework>
diff --git a/RDFSharp/RDFSharp.csproj b/RDFSharp/RDFSharp.csproj
index 19da9d16..aa16b341 100644
--- a/RDFSharp/RDFSharp.csproj
+++ b/RDFSharp/RDFSharp.csproj
@@ -3,7 +3,7 @@
     <AssemblyTitle>RDFSharp</AssemblyTitle>
     <AssemblyName>RDFSharp</AssemblyName>
     <AssemblyVersion>$(Version)</AssemblyVersion>
-    <Version>3.8.1</Version>
+    <Version>3.9.0</Version>
     <Authors>Marco De Salvo</Authors>
     <Copyright>Marco De Salvo</Copyright>
     <Description>Lightweight and friendly .NET library for realizing Semantic Web applications</Description>