My suspicion is those two little tabs are suppose to limit how far the stat will open. Once the spring has pulled the valve past the tabs, they are working the wrong way.

The reason? The little kids that are making them messed something up, or the tab material wasn't made from the correct metrology and was maybe too soft, maybe both.

The reality: That is on par with the current industry standard.

What brand stats are those? I want to be sure I don't have those "quality thermostats" in my stuff. Thanks. Gene