Strange behavior of periodic columns

[iStrannik]

I came across a strange behavior in the periodic columns. Sometimes they don't return the value I expect.

Steps to reproduce

1. clone the repo
2. Add debug-string here
   debug_assert!(hash_flag == E::from(BaseElement::new(0)) || hash_flag == E::from(BaseElement::new(1)), "Hash_flag must be 0 or 1 but it is {hash_flag}");
3. build in debug mode and run ./target/debug/winterfell rescue
4. Get the error

thread 'main' panicked at examples/src/rescue/air.rs:99:9:
Hash_flag must be 0 or 1 but it is 12411149292880158513719697302446626514

In rescue hash_flag is defined to be zero or one. Why is it 12411149292880158513719697302446626514?
Is this expected behaviour?