The EA8500 is a dual-firmware device, as pointed out above. If you have only flashed OpenWrt once, the other firmware will still be the Linksys OEM firmware. The Linksys boot loader will switch to the other firmware if the boot "fails" before it is marked as a success after three tries. It will then try that firmware three times before trying the first again.
You should be able to invoke this by:
- Turning the router around so you have access to the power switch or power connector and can still see the "status" light (typically the power light).
- Turn the router on
- The router will probably do a "light test" in the first couple seconds
- The status light should start flashing rapidly in a couple seconds, for two seconds
- When you see that, cut the power to the router
- Repeat a total of three times (two additional times)
- Let the next boot complete and you should be running the "other" firmware, hopefully the Linksys OEM firmware
- Once running the Linksys OEM firmware, install the most-current Linksys OEM firmware that you download from the Linksys site, without any modifications, using the OEM GUI
- The router should now have two versions of the Linksys OEM firmware installed on it (and no OpenWrt)