JS execution differs with or without debugger

Let me start from a far.
Some code (calculation of oauth signature, plain JS code) which can be found here:
http://yadi.sk/d/FIKD_SvuMn2Xn
works fine in Qt 5.2.0

When I migrated to 5.2.1 I've found that the same code works wrong if you start application without debugger and works fine if you start it with debugger. First line of console output containts test result: true indicates success, false indicates failure.

Example output (with and without debugger):

Debugging starts
Starting /usr/lib/i386-linux-gnu/qt5/bin/qmlscene /home/qtros/tmp/BugJs/BugJs.qml -qmljsdebugger=port:47402,block
QML Debugger: Waiting for connection on port 47402...
SHA1 VM TEST: true
INPUT
GET&https%3A%2F%2Fapi.twitter.com%2F1.1%2Fhelp%2Ftest.json&oauth_consumer_key%3DrUeGDPrcxbYN6r63JA39Kg%26oauth_nonce%3DxtfecukgPBsplT3B%26oauth_signature_method%3DHMAC-SHA1%26oauth_timestamp%3D1397913135%26oauth_version%3D1.0 EoNvzuQ5gz0LhbbssK4B9e9REdlN52ngl6YoN6eUqrs&
---- HASH [244873781,152401157,-808588303,-528091848,2024073624]
---- BIN ARRAY [2071061517,-1477515593,-1358206371,2117602940,-285983832]
e3HkDafu5revC2pdfjgOfO70O6g=
The program has unexpectedly finished.
Debugging has finished

Starting /usr/lib/i386-linux-gnu/qt5/bin/qmlscene...
SHA1 VM TEST: false
INPUT
GET&https%3A%2F%2Fapi.twitter.com%2F1.1%2Fhelp%2Ftest.json&oauth_consumer_key%3DrUeGDPrcxbYN6r63JA39Kg%26oauth_nonce%3DxtfecukgPBsplT3B%26oauth_signature_method%3DHMAC-SHA1%26oauth_timestamp%3D1397913135%26oauth_version%3D1.0 EoNvzuQ5gz0LhbbssK4B9e9REdlN52ngl6YoN6eUqrs&
---- HASH [-45834576,-1957938940,-196943121,-798980955,-1225908018]
---- BIN ARRAY [324821241,95708462,-1166915692,1120568750,-614847528]
ffffiiiippppJJJJqqqqNNNNAAA=
/usr/lib/i386-linux-gnu/qt5/bin/qmlscene exited with code 0