Segmentation fault using QDate::fromString in multiple threads

Hi,

Disclaimer: This is my first issue here. Please let me know if anything is missing.

I've noticed that since version 5.12.0 one of my applications keeps crashing on macOS.
After some digging, I found that it was due to QDate::fromString.
I could reproduce this issue on linux with the help of ASan.

In my application I get a "double free" error. Using the minimal example attached I always get a segmentation fault.

Attached is main.cpp containing a sample program which parses strings using QDate::fromString in parallel. For the crash messages see the attached "error.txt"

My application on the other hand crashes with following message (I wasn't able to reproduce this warning using a minimal example, yet):

==9913==ERROR: AddressSanitizer: attempting double-free on 0x60200005e9d0 in thread T19 (Thread (pooled)):
{{ #0 0x7f2a3d6d8640 in operator delete(void*) (/usr/lib/x86_64-linux-gnu/libasan.so.5+0xf0640)}}
{{ #1 0x7f2a39c712d4 in QDateTimeParser::~QDateTimeParser() tools/qdatetimeparser.cpp:64}}
{{ #2 0x7f2a39c11411 in QDate::fromString(QString const&, QString const&) tools/qdatetime.cpp:1344}}

Any help is appreciated.

Regards,

Andre