Enabling OpenVPN float?

I use OpenVPN to keep stuff secure, as half the time I am using a wifi network I don't actually own or control. Recently I switched ISP's, and now OpenVPN refuses to work. What's happening is the traffic appears to be coming from a different IP address about one out of every three times, causing OpenVPN to raise a security error and cancel the connection initiation.

I can fix this by adding the "–float" flag to OpenVPN, telling it to accept data from any IP address as long as it passes all other authentication tests, but is this really secure? I believe that if they really were trying to snoop on stuff they could spoof the IP address when resending it to me and I'd never know, so is there really any danger in running with the –float flag? If it's passing all other "authentication tests", then I assume that means they havn't tampered with anything else? Can anyone think of any cause for the IP to be different?

I'm assuming it's simply some routing screw up at the new ISP, but I thought I'd double check with you guys here. Opinions appreciated, as always ;)

I don't know a whole lot about vpn, but the ISP will sometimes change the ip because of routing issues. Also, because they probably use a mesh topology it could be coming from any route.

Your authentication key's will still be unique and private so they won't see whats going on. Only that there IS going on… ;)

Yeah, that's what I thought. Thanks for the responses guys.