LNK2005 error in debug mode only - c++

Question

Usually I eventually manage to sort out these LNK2005 (symbol already defined in object) errors but this one has me beat. I have a VS2010 solution containing several projects among them a project outputting an executable. This executable depends on libraries contained within the same solution thus I have added them into the "References" list for the executable project so that they get linked in automatically.
Now what happens when I try to build my executable (Server.exe) is that everything builds successfully when the release configuration is selected, but if I switch over to debug I get the following LNK2005 error:
error LNK2005: "public: class ACE_SOCK_Stream & __thiscall ACE_Svc_Handler<class ACE_SOCK_Stream,class ACE_NULL_SYNCH>::peer(void)const " (?peer#?$ACE_Svc_Handler#VACE_SOCK_Stream##VACE_NULL_SYNCH####QBEAAVACE_SOCK_Stream##XZ) already defined in Shell.obj network.lib(network.dll) Server (server\Server)
As can be seen in the error the projects use the ACE library.
I have had a look at ACE_Svc_Handler<class ACE_SOCK_Stream,class ACE_NULL_SYNCH> that is mentioned in the error and found out that one exported class in the network.dll inherits from it:
class DLL_API NetHandler : public ACE_Svc_Handler < ACE_SOCK_STREAM, ACE_NULL_SYNCH >
{
...
}
...and in the Server.exe there is also one class inheriting from it:
class Shell : public ACE_Svc_Handler < ACE_SOCK_STREAM, ACE_NULL_SYNCH >
{
...
}
The peer() method mentioned in the error is then used by both the NetHandler and Shell classes.
I am not sure if, and if so why, this would cause a LNK2005 error? What confuses me even more is that I only get the linker error in debug mode. I should also mention that the NetHandler class exported by network.dll is not used by the Server.exe, other projects that also depend on the network.dll do however.
Any ideas what could be causing this and how it can be solved? I am not sure where I should continue to investigate.
UPDATE: If I don't export the NetHandler class in my network.dll the linker error goes away, but I need to export that class.
UPDATE 2: I found this link in a different question about LNK2005 and although the link doesn't describe my scenario exactly I tried the proposed solution and I managed to get rid of the linker error if I place the following line before class Shell... in my Server.exe project:
extern template class __declspec(dllimport) ACE_Svc_Handler < ACE_SOCK_STREAM, ACE_NULL_SYNCH >;
So what does this line do exactly? Does it tell the Server project to not define ACE_Svc_Handler < ACE_SOCK_STREAM, ACE_NULL_SYNCH > itself but instead import it from one of the linked in libraries?