sqlfluff: `sqlfluff fix` corrupts Jinja for loop

Expected Behaviour

Output should be semantically equivalent to input, and have valid syntax.

Observed Behaviour

Output seems to be corrupted.

Steps to Reproduce

$ printf 'SELECT\n    1,\n{%% for _ in [1, 2, 3] %%} 2,{%%endfor %%}\n' |  sqlfluff fix -
Unfixable violations detected.
SELECT
    1,
    {% for _ in [1, 2, 3] %}
 {%endfor %}

Note that the contents of the for loop was completely deleted.

Slightly varying the input causes the output to be corrupted in other ways (e.g. 2 is present but the comma is not, or the 2 is duplicated multiple times).

Dialect

None specified

Version

SQLFluff ce4e5a344526f7ee61a0950adc079e4d3b5af438, Python 3.9.7

Configuration

None