Strange crashes with std::vector push_back() and emplace_back()

Hi,
some premises first:
-I have no proper debugging skills, plus I have some strict work timelines=
 (being into dsp coding) and cannot materially afford to open a "sub-chapte=
r" and drift to investigate this problem too much=2E Plus, I cannot materia=
lly provide any final code to replicate the crashes, since the code I am pr=
oviding is part of a music plugin; therefore, I am unable to open any offic=
ial ticket (in case it is about a bug at all)=2E
-For the reasons above, my message has to be taken as an inquiry to know i=
f anybody is aware of possible bugs involving relocations in std::vector, o=
r if anyone has an idea of why I am getting crashes=2E

I apologize in advance in case it's me who simply overlooked some deep asp=
ect of C++ of course=2E=2E=2E

-- Illustration of the issue --

I am using winlibs msvcrt (gcc 16=2E4=2E0 but gcc 14=2E2=2E0 had the same =
issue), windows 10 x64, i7 8770, codeblocks=2E
I am using -O3 but I am getting crashes even without any -O option=2E
The plugin is technically assembled as a DLL and uses static linking for t=
he C++ libs=2E

I have this (simplified) code:


class MsgRow // Made as a class so it gets initialized properly on instant=
iation
{
public:

	bool clear =3D false;
	bool dsp =3D false;
	wchar_t chars[50] =3D {};
};



class MyPlugin
{
public:

	void enqueueMessage(void *event)
	{
		if(!event) return;

		MsgRow new_row;
   // filling new_row fields here

		messages_=2Epush_back(new_row); // this crashes
	}

   // more methods

private:

	std::vector<MsgRow> messages_;

   // more stuff

}


What happens is that when enqueueMessage() is called with a valid event pt=
r, I get random crashes when push_back() is invoked=2E

If I rearrange the code to do the same using emplace_back():

auto& new_row =3D messages_=2Eemplace_back();
// set up new_row fields

=2E=2E=2EI still get random crashes when emplace_back() is called=2E

On the contrary, if I do (that's stupid but very illustrative):

MsgRow new_row;
// set up new_row fields here
messages_=2Eresize(messages_=2Esize()+1);
messages_=2Eback() =3D new_row;

=2E=2E=2Eit apparently works without crashing !!

More clues:

If in MyPlugin::ctor (not shown) I do:

messages_=2Ereserve(10); // 10 seems enough

=2E=2E=2Eboth push_back() and emplace_back() work without apparently crash=
ing=2E

Also, if before calling push_back() or emplace_back() I call messages_=2Ec=
apacity() and I intercept its return value for debugging, I see a bogus (ra=
ndom, often even negative) huge value

I am very puzzled=2E=2E=2E
Thanks for any hint=2E