I am making the transition to v3 and have come across something I don't understand. After applying an MPO to an MPS using `applyMPO`

, I try to add the new MPS to another, unmodified MPS. My code fails at the `plusEq`

operation on these two MPS, with the following message.

```
L = ITensor ord=2: (3|id=780|n=1,Site)' (2|id=376|l=1,Link)'1254313
{norm=0.00 (Dense Real)}
R = ITensor ord=2: (3|id=780|n=1,Site) (2|id=376|l=1,Link)'1254313
{norm=1.00 (Dense Real)}
From line 1006, file itensor.cc
ITensoITensor::operator+=: different index structure
ITensoITensor::operator+=: different index structure
```

I see the problem in the output -- there's a prime on the L tensor that doesn't match the same site on the R tensor. But I don't understand why it should be there, since I haven't primed anything in my code. Any help appreciated!