Massive qdebug() slowdown in "Run" mode in 3.5+

For the simple progam below qtcreator 3.4.1 takes 4.5 seconds to output text in Run mode (debug build) and 3.5 takes 23 seconds. Both versions take the same amount to produce output if launched as Debug and this time is ~120ms

2 Questions:
1) Why is Run mode significantly slower?
2) Why is Run mode 5 times slower in 3.5?

My application produces walls of tracing code in certain modes and this slowdown nearly makes "Run" unusable.

#include <iostream>
#include <chrono>
#include <QDebug>

int main()
{
auto start = std::chrono::steady_clock::now();
for (size_t i = 0; i < 100000; ++i)

Unknown macro: { qDebug() << "This is line number}

auto end = std::chrono::steady_clock::now();

qDebug() << "Output took: " << std::chrono::duration <double, std::milli> (end - start).count() << " ms\n";
}