Program crashes after the second approach of compile

To reproduce:

1. Start application and solve any task.
2. Try to solve any more. Then the program crash.

Backtrace:

0 QTextEngine::shapeTextWithHarfbuzz(int) const /usr/lib/libQtGui.so.4 0 0x4cc840
1 QTextEngine::shapeText(int) const /usr/lib/libQtGui.so.4 0 0x4cd095
2 QTextEngine::shape(int) const /usr/lib/libQtGui.so.4 0 0x4cd4d4
3 QTextLine::layout_helper(int) /usr/lib/libQtGui.so.4 0 0x4d85ca
4 QTextLine::setNumColumns(int) /usr/lib/libQtGui.so.4 0 0x4d91d2
5 QTextLayout::endLayout() /usr/lib/libQtGui.so.4 0 0x4d93c1
6 QLineControl::updateDisplayText(bool) /usr/lib/libQtGui.so.4 0 0x6bb87b
7 QLineControl::finishChange(int, bool, bool) /usr/lib/libQtGui.so.4 0 0x6be178
8 QLineControl::internalSetText(QString const&, int, bool) /usr/lib/libQtGui.so.4 0 0x6be4cd
9 QLineEdit::setText(QString const&) /usr/lib/libQtGui.so.4 0 0x6b65fd
10 Tester::run() 0 0x8050fff
11 ?? /usr/lib/libQtCore.so.4 0 0xc0cda2
12 start_thread pthread_create.c 304 0xe43e99
13 clone clone.S 130 0x10545fe

SIGSEGV on 473 in:

0x004cc827 <+2055>: mov -0x760(%ebp),%edx
0x004cc82d <+2061>: mov -0x4e4(%ebp),%esi
0x004cc833 <+2067>: mov 0x50(%edi),%eax
0x004cc836 <+2070>: mov -0x740(%ebp),%edi
0x004cc83c <+2076>: mov 0xc(%edi,%edx,1),%ecx
0x004cc840 <+2080>: mov 0x18(%eax),%edi
0x004cc843 <+2083>: lea 0x0(,%ecx,4),%edx
0x004cc84a <+2090>: add %edx,%edi
0x004cc84c <+2092>: mov %edi,-0x728(%ebp)
0x004cc852 <+2098>: mov 0x1c(%eax),%edi
0x004cc855 <+2101>: add %edx,%edi