Ed here at the house we just have unground outlets (built in 50's) except for one outlet I installed for my computer that I ran new wiring to with ground. Using the un-grounded CID was all over the place, worked sometimes, sometimes didn't I tried all kinds of resets different KSU the whole 9 yards. When I got an extention cord and plugged it into my grounded outlet, no more CID problems. Has to do with the KSU not the way CID is delivered. Can't tell you why just know what happened. I thought it was a system flaw for quite awhile, until I said well this shouldn't matter but it did.

Going to add it still doesn't make sense since it's 2 and a ground to a step down transformer. I just know it cleared the CID issue I was having with 3 different ksu's and several phones.

Retired phone dude