That's actually by design... ;- )
The 2610-series is limited Layer-3. One of their limitations is that there is a maximum of six static routes.
You have three manually defined; you already have three VLAN's with an IP-adddress. Those routed VLANs probably count as one static route each, I have never tried this setup myself.
So adding your fourth routed VLAN will add a seventh static route, which is not applied. Doesn't your log (at the time you created VLAN4) give a clou ?
If you want to test this theory: remove one of the IP-adresses on the other VLANs, or remove one of the static routes. I'm not sure whether VLAN 4 should immediately start routing, but I would think so.