GetModuleHandleEx does not work when called from DLL, only from EXE

I have some Win32 code that tries to load a module with

HMODULE hModule = NULL;
// "mydll" can be even "user32.dll"/"user32"
BOOL result = GetModuleHandleEx(GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT, "mydll", &hModule);

When I run this in the debugger from another DLL it fails in the GetModuleHandleEx call with

 0xC0000005: Access violation executing location 0x0000FDEE.

Even though the debugger shows that the module is loaded. However If I put exactly the same call in the EXE code, then it works fine.

The documentation does not seem to indicate this cannot be called from DLLs (see http://ift.tt/1CeCRQc)

NOTE: same happens for GetModuleHandle :(

Is there any reason why this does not work from DLL?