MonoDevelop を使用して MonoTouch ソリューションを作成したところ、編集のために XCode で xib を開こうとすると、次の例外が発生します (そして xib は開きません)。
System.NotSupportedException: Custom attribute type 0x43 is not supported.
at ICSharpCode.NRefactory.TypeSystem.CecilLoader+BlobReader.ReadCustomAttributeFieldOrPropType () [0x00000] in <filename unknown>:0
at ICSharpCode.NRefactory.TypeSystem.CecilLoader+BlobReader.ReadNamedArg (IType attributeType) [0x00000] in <filename unknown>:0
at ICSharpCode.NRefactory.TypeSystem.CecilLoader+CecilResolvedAttribute.DecodeBlob (System.Collections.Generic.List`1 positionalArguments, System.Collections.Generic.List`1 namedArguments) [0x00000] in <filename unknown>:0
at ICSharpCode.NRefactory.TypeSystem.CecilLoader+CecilResolvedAttribute.DecodeBlob () [0x00000] in <filename unknown>:0
at ICSharpCode.NRefactory.TypeSystem.CecilLoader+CecilResolvedAttribute.get_PositionalArguments () [0x00000] in <filename unknown>:0
at MonoDevelop.MacDev.ObjCIntegration.NSObjectInfoService.ConvertType (MonoDevelop.Ide.TypeSystem.ProjectContentWrapper dom, ITypeDefinition type) [0x00000] in <filename unknown>:0
at MonoDevelop.MacDev.ObjCIntegration.NSObjectInfoService+<GetRegisteredObjects>c__Iterator2.MoveNext () [0x00000] in <filename unknown>:0
at MonoDevelop.MacDev.ObjCIntegration.NSObjectProjectInfo.Update () [0x00000] in <filename unknown>:0
at MonoDevelop.MacDev.ObjCIntegration.NSObjectProjectInfo.Update (Boolean force) [0x00000] in <filename unknown>:0
at MonoDevelop.MacDev.XcodeSyncing.XcodeProjectTracker.UpdateTypes (IProgressMonitor monitor) [0x00000] in <filename unknown>:0
ただし、アプリケーションはコンパイルされ、正常に実行されます....