QWebView logouts while surfing

[Qiieha]

Hi guys,
I have a problem and need your help. I work with Qt 4.8.1
The problem:
I have one instance of QWebView and I set an url. Everything works and the page is loaded. The loaded WebApp requires login and uses cookies.
After login the user can navigate through the webapp. After several navigations (variable) the session seems to expire and the login page appears.

I tried a lots of things. I receive the cookie through QNetworkCookieJar and can read it.
The raw format of the cookie looks like this: JSESSIONID=C419FDE26FE26E68988AE3D6E3D90D77; secure; HttpOnly; domain=xxx.yyyy.com; path=/share/

So the cookie is there, but the session is lost after some navigations. Maybe you can give me a hint what's the problem. It's just one instance of QWebView and one WebApp!

And server config says, that a sessioncookie expires after one hour. On FireFox or Chrome it works as expected.

It would be very nice to solve this problem,
thank u