Trinitycore: [7x]worldserver.exe crash with releaseModelInstance

[cbcs]

Description:
I do not know what happened.look crash logs plz
Current behaviour: (Tell us what happens.)
I do not know what happened.look crash logs plz
Expected behaviour: (Tell us what should happen instead.)
I do not know what happened.look crash logs plz
Steps to reproduce the problem:
void VMapManager2::releaseModelInstance(const std::string &filename)
{
//! Critical section, thread safe access to iLoadedModelFiles
std::lock_guard lock(LoadedModelFilesLock);

    ModelFileMap::iterator model = iLoadedModelFiles.find(filename);
    if (model == iLoadedModelFiles.end())
    {
        VMAP_ERROR_LOG("misc", "VMapManager2: trying to unload non-loaded file '%s'", filename.c_str());
        return;
    }
    if (model->second.decRefCount() == 0)
    {
        VMAP_DEBUG_LOG("maps", "VMapManager2: unloading file '%s'", filename.c_str());
        delete model->second.getModel();  // crash in here.
        iLoadedModelFiles.erase(model);
    }
}

Crashdmp Download here
227e32f7557b+_worldserver.exe_[2-1_18-5-7].txt

https://mega.nz/#!MlVHwYTT!iLLotkuULAP-OPCgj2aCTZxit8OLq3Z7Ahb_WGTAFE8

Branch(es): 3.3.5 / master (Tell us which branch(es) this issue affects.)
master
TC rev. hash/commit:
https://github.com/TrinityCore/TrinityCore/commit/26321d88d4c1e86b2ecb07cc2e3ac779c325a0cb
TDB version:
7.03
Operating system:
win7 x64

[jackpoz]

Some (maybe) useful data from the log:

Local std::string tilefile = "Data/vmaps/1220_24_31.vmtile"
std::string name = "7Nb_Nightborn_Shipramp01.m2"
Parameter unsigned int mapId = 0x4C4 (1220)

[Aokromes]

over a year since the last crash and vmaps system got rewriten after this, if this bug is still valid open a new ticket with updated core.

[jackpoz]

note: this should happen only with

GridUnload = 1

in the configs