@Fae Thanks for documenting this issue. Your post arrived just as I was writing mine.

I also use the ER605 in standalone mode, it is configured making extensive use of DHCP and ACL. The router is providing main internet access to my small business and as such cannot simply be turned...

I can confirm this behavior. I had to revert back to the previous firmware version. @Fae: please confirm and update with ETA for a fix.