I have implemented a modal in Zkoss with several slides, one of the modalPage has a slider componente with a related longbox. The two components use the same value like this:

<u:longbox
          id="longbox-input"
          value="@bind(viewModel.amount)"
          onChange="@command('updateValue')"
          onOK="@command('updateValue')"
          />
<u:slider
         id="slider-input"
         mold="sphere"
         width="100%"
         minpos="@load(viewModel.amountMinValue)"
         maxpos="@load(viewModel.amountMaxValue)"
         curpos="@bind(viewModel.amount)"
         onScroll="@command('updateValue')"
         />

When I am on the modalPage everything works as expected, in this way if I input some value in the longbox the value will be displayed on the slider and the other way around. When I change modalPage, the value in the longbox is correctly displayed, the slider value is correct but the position of the slider cursor is wrong even if the value of the amount is correct. Did you have something similar?