Tags are not being merged as expected

Given a CompositeResourceDefinition with the following property.

```yaml
tags:
x-kubernetes-map-type: granular
additionalProperties:
type: string
description: Key-value map of resource tags.
type: object
````

And a xr with the following field.

```yaml
tags:
my-label: test
```

And P&T func configured like the following

```yaml
- step: patch-and-transform
functionRef:
name: function-patch-and-transform
input:
apiVersion: pt.fn.crossplane.io/v1beta1
kind: Resources
resources:
- name: my-resource
base:
patches:
- type: FromCompositeFieldPath
fromFieldPath: spec.parameters.tags
toFieldPath: spec.initProvider.tags
```

The tags are being overwritten where I am expecting/hoping they will be merged.

Please advise.