If `addrProxy` or `addrSeparateProxyTor` do not have a colon in the string somewhere in the QSettings storage, then attempting to open the options dialog will cause the entire program to crash.

I'm not sure if this is really a problem since it is impossible to make those strings not have colons in them from normal operation. In order to replicate this, you must modify what QSettings stores (a conf file in Linux and Registry in Windows).
return fMinimizeToTray;
        case MapPortUPnP:
#ifdef USE_UPNP
            return settings.value("fUseUPnP");
#else
            return false;
#endif
        case MinimizeOnClose:
            return fMinimizeOnClose;
        
        case ProxyUse:
            return settings.value("fUseProxy", false);
        case ProxyIP: {
            
            QStringList strlIpPort = settings.value("addrProxy").toString().split(":", QString::SkipEmptyParts);
            return strlIpPort.at(0);
        }
        case ProxyPort: {
            
            QStringList strlIpPort = settings.value("addrProxy").toString().split(":", QString::SkipEmptyParts);
            return strlIpPort.at(1);
        }
        
        case ProxyUseTor:
            return settings.value("fUseSeparateProxyTor", false);
        case ProxyIPTor: {
            
            QStringList strlIpPort = settings.value("addrSeparateProxyTor").toString().split(":", QString::SkipEmptyParts);
            return strlIpPort.at(0);
        }