htmlb:tray is expanded again when page is reloaded

I have created several trays on one page. I did define the tray as follow.

<htmlb:tray id = "tray3"

title = "Declaratie gegevens"

design = "BORDERLESS"

width = "90%"

isCollapsed = " ">

</htmlb:tray>

When the user decides to collapse the tray everything is working fine. But as soon as a server event is triggered the tray is expanded again when the page is reloaded.

Of course, I did look at bsp program SBSPEXT_PHTMLB but this example is based on a flowlogic page. I'm building a bsp application based on the MVC model.

What kind of event can be triggered by the onCollapse of onExpand attribute of the htmlb:tray tag?

Please help me finding a solution to memorise whether or not the tray is collapsed or expanded before the server event is triggered.

Best regards,

Sander Pol