h2o-wave: ui event without ui update

Question

I would like to respond to a button click without updating or changing the ui (e.g. just do a print() for now). If I try with h2o-wave v1.0.2 on Win10-22H2, the ui seems to hang in an infinite loading spinner.

This behavior only applies to mode='unicast', which is the default. In case of mode='multicast' and mode='broadcast', the ui and the app behave as expected (i.e. print() works fine, ui stays responsive).

The problem seems to be independent of browser (tried with Firefox 122.0.1 and MS-Edge 121.0.2277.112).

In the following boilerplate, every works fine, i.e. print() and ui updates happen as expected:

from h2o_wave import main, app, Q, ui

@app('/buttons', mode='broadcast')
async def serve(q: Q):
    if not q.client.initialized:
        q.page['form'] = ui.form_card(box='1 1 2 2', items=[
            ui.buttons([
                ui.button(name='btn1', label='BTN-1'),
                ui.button(name='btn2', label='BTN-2')
            ]),
            ui.text_m(name='text', content='Click on a button ...'),
        ])
        q.client.initialized = True
    if q.args.btn1:
        print(f'{q.args.btn1=}')
        print(f'{q.args.btn2=}')
        q.page['form'].text.content = 'btn1 was pressed.'
    if q.args.btn2:
        print(f'{q.args.btn1=}')
        print(f'{q.args.btn2=}')
        q.page['form'].text.content = 'btn2 was pressed.'
    await q.page.save()

If line q.page['form'].text.content = 'btn1 was pressed.' is removed, the ui seems to hang in an infinite loading spinner (tried to post an image, but I am new on stackoverflow hence not yet allowed).

This holds true indipendent of applying await q.page.save() or not.

The application works fine as soon as I use mode='multicast' or mode='broadcast' (which is not what I need in my case).

What would be the correct way in mode='unicast' to handle a button click without updating the ui?