Source code not displayed while debugging an external library

I have a project which consists of a library and an application. Library is built as a debian package and installed (with -dbg package).
When i load the application using library in QtC and debug it, the debugger does not display source code in the library.
GDB on command line does that.

This may be a difficult one to reproduce but you can try on a Ubuntu system:

git clone https://github.com/vranki/libsiilihai.git
git clone https://github.com/vranki/siilihai-client.git
cd libsiilihai
dpkg-buildpackage -rfakeroot -b
sudo dpkg -i ../libsiilihai*.deb

Now open siilihai-client.pro in QtC and build it.
Add a breakpoint to for example LoginWizard::LoginWizard

Start debugging, debugger should break at breakpoint.

Notice that Frame #2 (ClientLogic::lanchSiilihai() ) is displayed as gray
in backtrace and clicking on it displays assembler instead of source code.

If you do the same in GDB, the source for frame #2 is displayed.