immediate crash in QtConcurrent

I am running qt5 from git, the stable branch. (qtbase is at c819a8926959)

After upgrading my concurrent-heavy tool I got a crash (most of the time).
A simple investigation showed that I got a crash briefly after this;

QList<Foo*> usedRelations;
QFuture<void> relationsFuture = QtConcurrent::map(
usedRelations, normalizeRelation);

usedRelations had 113 items in it.

Gdb output;

[New Thread 0x7fffcffff700 (LWP 23529)]
[New Thread 0x7fffcf7fe700 (LWP 23530)]
[New Thread 0x7fffceffd700 (LWP 23531)]
[New Thread 0x7fffce7fc700 (LWP 23532)]
[New Thread 0x7fffcdffb700 (LWP 23533)]
[New Thread 0x7fffcd7fa700 (LWP 23534)]
[New Thread 0x7fffccff9700 (LWP 23535)]
[New Thread 0x7fffabfff700 (LWP 23536)]

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffceffd700 (LWP 23531)]
0x00007ffff60d06cc in void std::__introselect<double*, long>(double*, double*, double*, long) ()
from /home/zander/work/build-qt5/installed/lib/libQt5Concurrent.so.5
(gdb) bt
#0 0x00007ffff60d06cc in void std::__introselect<double*, long>(double*, double*, double*, long) ()
from /home/zander/work/build-qt5/installed/lib/libQt5Concurrent.so.5
#1 0x00007ffff60d010b in QtConcurrent::BlockSizeManager::timeAfterUser() ()
from /home/zander/work/build-qt5/installed/lib/libQt5Concurrent.so.5
#2 0x000000000046e79d in QtConcurrent::IterateKernel<QList<OsmParsedRelation*>::iterator, void>::forThreadFunction (this=0x7fffe40ddd80) at ../../installed/include/QtConcurrent/qtconcurrentiteratekernel.h:231
#3 0x000000000046d37a in QtConcurrent::IterateKernel<QList<OsmParsedRelation*>::iterator, void>::threadFunction (this=0x7fffe40ddd80) at ../../installed/include/QtConcurrent/qtconcurrentiteratekernel.h:192
#4 0x00007ffff60cf685 in QtConcurrent::ThreadEngineBase::run() ()
from /home/zander/work/build-qt5/installed/lib/libQt5Concurrent.so.5
#5 0x00007ffff5093342 in ?? () from /home/zander/work/build-qt5/installed/lib/libQt5Core.so.5
#6 0x00007ffff5095bf3 in ?? () from /home/zander/work/build-qt5/installed/lib/libQt5Core.so.5
#7 0x00007ffff4b8fe0e in start_thread (arg=0x7fffceffd700) at pthread_create.c:311
#8 0x00007ffff40ad9ed in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:113

If I do a git-revert of 3567f4c2fc9ee45898ed9a0784051d4fa64897e2,
the crash disappears.