frozen pipes acting weird


My bathroom pipes (facing the prevailing winds) froze last night. I noticed when I was trying to figure the extent of the damage that when I turned on the cold water tap on the lav, the other lav and the shower BOTH went on!
In detail:
I turned on the hot water taps of both lavs and the shower. A few drips came out, then ceased. Given the temps, I just knew we had a frozen pipe nearby under the house. This has happened before and always thawed.
To check, I turned on the cold water tap on the right hand lav. The HOT water taps of the left hand lav and the shower immediately started flowing full force! -- with icy water. Never did warm up.
I repeated using the lefthand lav cold water tap. Same thing: the righthand lav and shower both flowed with cold water. The only tap that was on in both was the HOT water tap.
I repeated with the shower tap. Nothing happened. The cold water tap in the shower worked, but didn't trigger the HOT water taps of the lavs.
The lavs are further out from the main and from the hot water heater by about five feet, against an exterior wall facing the prevailing winds. The shower is interior, accessible by a panel in an interior wall.
Why on earth does turning on a cold water tap trigger cold water flow in a hot water tap??
btw, the pipes had not burst. I set a heater under the house to thaw the pipes and it worked well. All is back to normal now, with hot water taps providing hot water in all three locations and cold water not triggering flow in any other faucet.
Is my plumbing possessed??
Katherine Bryce Santa Fe NM USA
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kbryce wrote:

The faucet where you turned on the hot and cold water backfed the hot water pipe to the shower.
D
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put a sneaky dotted line across the hot and cold faucets at:
http://www.ccis.com/home/mnemeth/plumbing/blkdia1.gif
kbryce wrote:

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