Gallery block: duotone settings lost between transforms

[glendaviesnz]

Description

With the refactored gallery block, when duotone is set for an image, this setting is lost of the Gallery is transformed to a different format, and does not return if the transform is undone.

It may not be possible to do anything about this as it will most likely be dependent on the block being transformed to being able to support duotone - but should at least work when transforming between core gallery and core image blocks.