Karabo 2.19.0: not allowed to configure output channel

Not sure what exactly upsets the framework, but somehow:

2023-12-04T15:54:37.690 WARN  karabo.devices.GuiServerDevice  : Instantiating device 'CALDEV_HAMMERD/AGIPD/CORRECT00_Q1M1' failed: Configuring output channel schema is not allowed: 'dataOutput.schema'

It seems related to something inside the XTDF output schema being applied during

OUTPUT_CHANNEL(expected)
.key("dataOutput")
.dataSchema(AgipdCorrection._base_output_schema)
.commit(),

Same thing happens when trying to start a JungfrauCorrection.

I'll try to narrow down where things go sour.