What happened?

When handling flatten, prism overwrites the coders of its input pcollections with the flatten's output coder by changing the coder mapping(coder id -> coder proto). In this case, if the same coder id is also referred by a separate pcollection that has nothing to do with the flatten, the underlying coder proto for this pcollection is also changed.

https://github.com/apache/beam/blob/release-2.64/sdks/go/pkg/beam/runners/prism/internal/handlerunner.go#L115

Issue Priority

Priority: 2 (default / most bugs should be filed as P2)

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