ExdiGdbSrv.dll BufferWrapper.h assert

I'm exercising !uefiext.init command over EXDI and WinDbg pops up a assert dialog many times as attached.

I build my own ExdiGdbSrv.dll, attach to EngHost.exe to get this callstack:

>	ExdiGdbSrv.dll!common_assert_to_message_box<wchar_t>(const wchar_t * const expression, const wchar_t * const file_name, const unsigned int line_number, void * const return_address) Line 388	C++
 	ExdiGdbSrv.dll!GdbSrvControllerLib::BufferWrapper<char>::SetLength(unsigned __int64 newLength) Line 74	C++
 	ExdiGdbSrv.dll!GdbSrvControllerLib::GdbSrvController::GdbSrvControllerImpl::ReadMemory(unsigned __int64 address, unsigned __int64 maxSize, const GdbSrvControllerLib::memoryAccessType memType) Line 1677	C++
 	ExdiGdbSrv.dll!GdbSrvControllerLib::GdbSrvController::ReadMemory(unsigned __int64 address, unsigned __int64 size, const GdbSrvControllerLib::memoryAccessType memType) Line 3438	C++
 	ExdiGdbSrv.dll!CLiveExdiGdbSrvServer::ReadVirtualMemory(__int64 Address, unsigned long dwBytesToRead, tagSAFEARRAY * * pbReadBuffer) Line 537	C++
 	[External Code]	
 	uefiext.dll!FindModuleBackwards(unsigned __int64 Address) Line 81	C++
 	uefiext.dll!findall(IDebugClient4 * Client, const char * args) Line 256	C++
 	[External Code]	
 	uefiext.dll!uefiext_init(IDebugClient4 * Client, const char * args) Line 241	C++
 	[External Code]	

The point of interest is this line of code in GdbSrvControllerLib.cpp:

        size_t maxReplyLength = (maxSize * 2) + 256;
        if (!result.TryEnsureCapacity(maxReplyLength))
...		
                    result.SetLength(result.GetLength() + 1);

Why set 'result' length to larger than initialized?