I've got also the same problem. I don't know exatly whats causing it but I found from the Wiki a propable source for the connection problem. So I figured it could be the power-saving option in the WLAN connection's additional settings (Settings -> Internet conenctions -> Connections -> Edit "your connection" -> Advanced -> Other -> Power saving). As the Wiki suggests, all routers don't support this option and therefore the connection is lost if not used.

Because I don't want to buy a new router, I've set AutoDisconnect to cut of my home-wlan if it's not used. Don't really know is this the reason for the problem but this solution makes a difference beacause I don't have to manually connect-disconnect the wlan every time I want to use it.

EDIT: And when I fiddled with the settings I noticed the connection is not halting when the power-saving mode is off, but it drains the battery pretty quickly..