'on' is not a boolean

When using the OMV (3.0.81 Erasmus) web UI from Chrome I get failures when submitting forms with checked checkboxes, e.g. when trying to enable a service such as NFS. The error messages are typically something like:
Exception 'OMV\Json\SchemaValidationException' with message 'enable: The value 'on' is not a boolean.'

The stack trace indicates the exception occurs in schema.inc:
OMV\Json\Schema->validateBoolean('on',Array,'enable')

I don't get this problem when doing the same from Firefox. I assume Chrome is sending the value 'on' for checked checkboxes and failing, whereas Firefox is sending '1' or 'TRUE' or something and succeeding.

Is this a known issue with a recommended workaround?

Aha - thanks! I had tried <ctl>F5 hard refresh, using an Incognito window and running with Developer Tools open. I thought that would eliminate caching issues, but evidently not.

What would it have been, out of interest: an old version of a Javascript resource that converts 'on' to 'TRUE' or something?