@ArraySchema with items inheriting from an abstract base class not generating properly

I have the following lists annotated with @ArraySchema, and they're meant to hold subtypes of an abstract class. The openapi generated for each list is different. I would like to know how to achieve the second list's config, but without the unbound wildcard. I'm not sure what I'm doing wrong.

@ArraySchema(schema=@Schema(type="object", description = "description", oneOf = {SubType1.class}))
List<AbstractType> foo;
@ArraySchema(schema=@Schema(type="object", description = "description", oneOf = {SubType1.class}))
List<?> bar;

The abstract class's type hierarchy is fairly simple:

// AbstractType.java
public abstract class AbstractType {
    protected CommonField field;
}

// SubType1.java
public class SubType1 extends AbstractType {
    private String baz;
}

The generated OpenApi:

"foo":
{
    "type": "array",
    "items":
    {
        "$ref": "#/components/schemas/AbstractType"
    }
},
"bar":
{
    "type": "array",
    "items":
    {
        "type": "object",
        "description": "description",
        "oneOf":
        [
            {
                "$ref": "#/components/schemas/SubType1"
            }
        ]
    }
}