It happened a few times. What matters is the depth and length of the inversion. So it’s not the fact that it happened, but a sustained economic condition which brings it about.

This time the reversal is due to a different factor, namely the foreign central banks who have hundreds of millions of dollars they need to invest. They got those dollars when they exchanged their manufacturers’ dollars for yen, yuan, baht, etc. They don’t want to convert the dollar into their own currency because that would make it appreciate, so they invest it back in the US.

This glut of dollar looking for Treasury debt raises demand, pushing down yields.

So, the more we import, the lower our long term bonds get.

The last few months, the trend is for imports to become a little less. So eventually the bond curve will normalize, and then we will see 30 year mortgages go up.