I've made some good progress on my ECM-1240 interface. It's a good thing I'm running it on xPLserial, where I can easily make changes to the script instead of having to recompile if it were an application. I found some problems in my script that caused it to miss a byte here or there and seems to be the source of the instability I was seeing. The current script has been running for 5.5 hours (since a power outage ended this morning) without having to reset the counters.
My script is no longer sending the readings over xPL, instead it's doing direct writes to MySQL. It was a pain trying to get ODBC working with XP Embedded, but eventually I did find an ODBC add on for HP thin clients. It doesn't say it supports the T5700, but it works anyway. Now, I'm updating power usage everytime it changes instead of whenever the xPL message was received.
As for this morning's blackout, it was quite a racket. I was awaken around 4AM to a symphony of beeping UPS's - 9 of them to be exact. I really need to open up a few of them and cut the buzzer wires. Some are really way too loud. I also discovered a couple with dead batteries. Good thing I got a couple more UPS's on Black Friday. It's actually cheaper to replace the low end ones instead of buying new batteries.