Boolean filters don't work for Cloud Datastore?

I have a query with Google Cloud Datastore as the data source. I want to add a single filter based on a boolean value:

However it returns no results when setting true or false (or Javascript notation e.g. {{true}}). Filtering on string fields works as expected.

Here is the same query run in Cloud Datastore - it returns results:

It seems like boolean filters don't work for Cloud Datastore, meaning I need to either use a Transformer to do the filtering (query is then very slow) or I need to create a new string field to filter on, neither of which are nice options.

Has anyone else got boolean filters working for Cloud Datastore queries?

have you tried putting the original "true" in the where statement in brackets? {{true}}

Thanks Steven. Yes I've tried that but it also returns no results.