One unit is wired, the other is wifi. Major lag in the wifi one (about 12 ft from the router, but through a wooden wall, on the 5GHz band--signal quality stable at about 87% strength as reported by the router). There was no visible sign of other 5GHz routers in the area as evidenced by a scan, but there could be other appliances generating interference that I could not see. That said, the problem went away 100% with reserved I.P. addresses.
The "m" entries in the log (nonsense, garbage) are a definite sign of some firmware issue. It could be as simple as a malformed message, or as bad as stack corruption--it's hard to tell, but there were a LOT of them. 5GHz signal was also dropping out periodically--say every 60 seconds or so for a small "blip"). Problems easy to reproduce without reserved IP addresses, but so far impossible to reproduce with reserved IP addresses, with the same wired/wifi mix (the only variable is the reserved IP)
Anyone reading this, however, should keep the perspective: this is the most stable router I've ever owned, bar none, and I've pretty much owned them all, not just Dlink. Don't let this petty problem dissuade you from it--the workaround is easy. (Even more amazing is that this is with the original 1.00 firmware.) It's a fine machine, a definite safe buy. Right now, I wouldn't even consider a fix for this to be a reason to update the firmware.
I have no big issues. BTW, I also have Ooma behind the router (no config necessary), plus use Cisco VPN software (which died a horrible death with my Cisco-branded unit, but works great on this router) to connect my network to the network at my workplace on several occasions this week.