Debugger misses some breakpoints hits

Debugger seemingly randomly misses hits of a breakpoint set at the beginning of a function.

Steps to reproduce:

• Open tests/manual/debugger/simple/simple.pro from the Qt Creator repo
• In simple_test_app.cpp:
  • Uncomment line 7214 containing qthread::testQThread();
  • Place a breakpoint at the very beginning of qthread::Thread::run() (line 4209)
• Start debugging; pay attention to the ID (or the name) of the thread when breakpoint is hit. Hits for some threads will not arrive.

Below are the results from a couple of my runs (x denotes a hit for the thread with the given ID):

ID    0  1  2  3  4  5  6  7  8  9 10 11 12 13
Run 1 x  x  x  x  x     x        x  x  x  x  x
Run 2 x     x  x     x  x     x  x     x  x  x
Run 3 x  x  x  x  x  x  x     x  x  x     x  x
Run 4 x  x     x  x  x  x        x  x  x  x  x
Run 5 x  x     x  x  x  x     x     x  x  x  x
Run 6 x  x        x  x  x           x  x  x  x

Interestingly enough, when placed further down the code of the function, breakpoints trigger for all threads as expected.