Domestic hot water

I have a boiler that supplies both heat and hot water. I've never had a problem with it until recently. We have a small home and not a lot of room for a washing machine,so my wife has always used the local laundramat(sp). Now that we're getting up there in age,she no longer wanted to that.
We bought a small apartment sized,single hose washing machine she attatches to our single handle Moen kitchen faucet.
Not every time,maybe every fourth or fifth time she uses the washer with the water mixed,when I go to take a shower later, I end up showering with nothing but the hot water tap on. It's warm,but not hot. It should be hot enough to almost scald you.
I know you'll wonder the obvious things,like the boiler isn't kicking on properly,or heating to the right temp,etc.,But I can assure you it's not the boiler.
It has something to do with mixing the water to the washer. When the washer is washing or draining,the water isn't being used but is sitting pressurized in the hose,back thru the faucet and into the pipes. What I'm thinking is, some sort of hydraulic loop develops when the hot and cold is sitting there pressurized.
Has anyone ever heard of or experienced anything like this? This only happens after using the washing machine.

When the faucet is on, with the mixer set to an intermediate position, the loop is there whether the washer is drawing water at that moment or not. If you turn with faucet OFF the loop is interrupted, and no cross-flow mixing of cold into the hot being drawn by other taps should occur. This could be prevented automatically by installing a check valve on the hot line to the sink to prevent reverse flow, but depending on the overall water distribution in the house you may want to put check valves on both.