C# UHT fails to recognize delegates declared in another class's namespace

This is a problem only with the new C# based UHT that comes with 5.1. This is code that has compiled fine since UE4.Disabling the new UHT using this made my code compile again.
<Configuration xmlns="https://www.unrealengine.com/BuildConfiguration">
<UEBuildConfiguration>
<bUseBuiltInUnrealHeaderTool>false</bUseBuiltInUnrealHeaderTool>
</UEBuildConfiguration>
</Configuration>

#pragma once
#include "ClassA.generated.h"
UCLASS(BlueprintType, Blueprintable)
class BLANK_API UClassA : public UObject
{
    GENERATED_BODY()
public:
    DECLARE_DYNAMIC_MULTICAST_DELEGATE(FSomeDelegate);
};

#pragma once
#include "ClassA.h"
#include "ClassB.generated.h"
UCLASS(BlueprintType, Blueprintable)
class BLANK_API UClassB : public UObject
{
    GENERATED_BODY()
public:
    UPROPERTY(BlueprintAssignable, Category = "Listeners")
        UClassA::FSomeDelegate OnDelegate;
};

Error: Unable to find 'class', 'delegate', 'enum', or 'struct' with name 'UClassA::FSomeDelegate'