ctor overload in that it succeeds in preserving the early-bound type identity and always loads the correct type, as written in code. Its implementation is correct around the typeof(). Which is basically the WPF's way of doing the same stuff. The solution? No ideal one, but in our case we were consuming the type conversions within our system only, so we picked the ValueSerializerAttribute instead. So it's no use writing a typeof() - it's always the plaintext-and-magic scenario inside. The real and correct runtime type reference is flattened into plaintext, and here there be dragons. If you use the second path, what could possibly go wrong? Well, actually the attribute only uses the first path. The attribute has two constructor overloads, one for a plaintext type specification (which is - not unexpectedly - pure magic at runtime) and one for an early-bound typeof() reference. The root of all evil is a flaw in the TypeDescriptorAttribute implementation. We've also observed this behavior in pluggable systems involving loading assemblies from outside the appbase folder. Return base.ConvertTo(context, culture, value, destinationType) If (destinationType = typeof(string) & value.GetType() = typeof(Test)) Public override object ConvertTo(ITypeDescriptorContext context, culture, object value, Type destinationType) Return base.ConvertFrom(context, culture, value) Public override object ConvertFrom(ITypeDescriptorContext context, culture, object value) Return base.CanConvertTo(context, destinationType) If (destinationType = typeof(Test) || base.CanConvertTo(destinationType)) Public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType) Return base.CanConvertFrom(context, sourceType) If (sourceType = typeof(string) || base.CanConvertFrom(context, sourceType)) Public override bool CanConvertFrom(ITypeDescriptorContext context, System.Type sourceType) Public override bool GetStandardValuesSupported(ITypeDescriptorContext context) Public class TestConverter : TypeConverter Object v = TypeDescriptor.GetConverter(typeof(MyTest.Test)).ConvertFromInvariantString('Test') edit - It looks like this is not working because of some quirk of loading assemblies dynamically - this code is running under a plugin like architecture. edit - this problem is almost certainly related to pieces being in different assemblies. edit - alternatively any suggestions on how I can debug the TypeDescriptor so I can see what is going on and then I can probably answer this myself. edit - this code seems to work when I run it in a console on its own, I'm actually calling a converter from within a much more complex application and from a different namespace. I can only assume I have made an obvious mistake but I cannot see it. I am trying to understand why the below code is not working as expected the TypeDescriptor is simply not picking up the custom converter from the attributes.

Opryzelp converter not working