Example "threaded" crashes on close on macOS

[pftbest]

$ cargo run --example threaded
    Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs
     Running `target/debug/examples/threaded`
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threaded(21712,0x7fffbe3103c0) malloc: *** error for object 0x7fb6ac459c30: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug

Process:               threaded [21712]
Path:                  /Users/USER/Downloads/*/threaded
Identifier:            threaded
Version:               0
Code Type:             X86-64 (Native)
Parent Process:        ??? [21711]
Responsible:           threaded [21712]
User ID:               501

Date/Time:             2017-04-23 16:10:13.067 +0300
OS Version:            Mac OS X 10.12.4 (16E195)
Report Version:        12
Anonymous UUID:        40C67DB0-96B3-5C62-3103-151A222FEC41

Sleep/Wake UUID:       7E6038B5-E5CD-457F-BAF1-9E5EDBF8469B

Time Awake Since Boot: 120000 seconds
Time Since Wake:       910 seconds

System Integrity Protection: enabled

Crashed Thread:        0  Dispatch queue: com.apple.main-thread

Exception Type:        EXC_CRASH (SIGABRT)
Exception Codes:       0x0000000000000000, 0x0000000000000000
Exception Note:        EXC_CORPSE_NOTIFY

Application Specific Information:
abort() called
*** error for object 0x7fb6ac459c30: pointer being freed was not allocated
 

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   libsystem_kernel.dylib        	0x00007fffb552cd42 __pthread_kill + 10
1   libsystem_pthread.dylib       	0x00007fffb561a5bf pthread_kill + 90
2   libsystem_c.dylib             	0x00007fffb5492420 abort + 129
3   libsystem_malloc.dylib        	0x00007fffb5581fe7 free + 530
4   org.qt-project.QtQml          	0x000000010e66238e QQmlPropertyCache::~QQmlPropertyCache() + 318
5   org.qt-project.QtQml          	0x000000010e66275e QQmlPropertyCache::~QQmlPropertyCache() + 14
6   org.qt-project.QtQml          	0x000000010e50cf59 QJSEnginePrivate::~QJSEnginePrivate() + 297
7   org.qt-project.QtQml          	0x000000010e60ced5 QQmlEnginePrivate::~QQmlEnginePrivate() + 1221
8   org.qt-project.QtQml          	0x000000010e69272e QQmlApplicationEnginePrivate::~QQmlApplicationEnginePrivate() + 14
9   org.qt-project.QtCore         	0x000000010f5fb878 QObject::~QObject() + 1880
10  org.qt-project.QtQml          	0x000000010e60e8fd QQmlEngine::~QQmlEngine() + 397
11  org.qt-project.QtQml          	0x000000010e6938ee QQmlApplicationEngine::~QQmlApplicationEngine() + 14
12  threaded                      	0x000000010dfcbb63 dos_qqmlapplicationengine_delete + 51
13  threaded                      	0x000000010dfc9da5 _$LT$qml..qmlengine..QmlEngine$u20$as$u20$core..ops..Drop$GT$::drop::h72a6fef9bce1804d + 37
14  threaded                      	0x000000010dfb57b1 core::ptr::drop_in_place::hd698f628d3b04aa3 + 17
15  threaded                      	0x000000010dfb970c threaded::main::hb4fe66955fd815d0 + 172
16  threaded                      	0x000000010dff08fb __rust_maybe_catch_panic + 27
17  threaded                      	0x000000010dfefd71 std::rt::lang_start::ha1f4f04346e51ef5 + 369
18  threaded                      	0x000000010dfba63a main + 42
19  libdyld.dylib                 	0x00007fffb53fe235 start + 1

Thread 1:: com.apple.NSEventThread
0   libsystem_kernel.dylib        	0x00007fffb552534a mach_msg_trap + 10
1   libsystem_kernel.dylib        	0x00007fffb5524797 mach_msg + 55
2   com.apple.CoreFoundation      	0x00007fff9fc9c4e4 __CFRunLoopServiceMachPort + 212
3   com.apple.CoreFoundation      	0x00007fff9fc9b971 __CFRunLoopRun + 1361
4   com.apple.CoreFoundation      	0x00007fff9fc9b1c4 CFRunLoopRunSpecific + 420
5   com.apple.AppKit              	0x00007fff9d8e52d2 _NSEventThread + 205
6   libsystem_pthread.dylib       	0x00007fffb56179af _pthread_body + 180
7   libsystem_pthread.dylib       	0x00007fffb56178fb _pthread_start + 286
8   libsystem_pthread.dylib       	0x00007fffb5617101 thread_start + 13

Thread 2:
0   libsystem_kernel.dylib        	0x00007fffb552d44e __workq_kernreturn + 10
1   libsystem_pthread.dylib       	0x00007fffb5617695 _pthread_wqthread + 1426
2   libsystem_pthread.dylib       	0x00007fffb56170f1 start_wqthread + 13

Thread 3:
0   libsystem_kernel.dylib        	0x00007fffb552d44e __workq_kernreturn + 10
1   libsystem_pthread.dylib       	0x00007fffb5617502 _pthread_wqthread + 1023
2   libsystem_pthread.dylib       	0x00007fffb56170f1 start_wqthread + 13

Thread 4:
0   libsystem_kernel.dylib        	0x00007fffb552d44e __workq_kernreturn + 10
1   libsystem_pthread.dylib       	0x00007fffb5617695 _pthread_wqthread + 1426
2   libsystem_pthread.dylib       	0x00007fffb56170f1 start_wqthread + 13

Thread 0 crashed with X86 Thread State (64-bit):
  rax: 0x0000000000000000  rbx: 0x0000000000000006  rcx: 0x00007fff51c500f8  rdx: 0x0000000000000000
  rdi: 0x0000000000000307  rsi: 0x0000000000000006  rbp: 0x00007fff51c50120  rsp: 0x00007fff51c500f8
   r8: 0x0000000000000000   r9: 0x0000000000000000  r10: 0x0000000008000000  r11: 0x0000000000000206
  r12: 0x0000000000000005  r13: 0x0000000000000005  r14: 0x00007fffbe3103c0  r15: 0x0000000000000000
  rip: 0x00007fffb552cd42  rfl: 0x0000000000000206  cr2: 0x00007fffbe2f2128
  
Logical CPU:     0
Error Code:      0x02000148
Trap Number:     133