Major Description
Currently, the collapsible state is only processed when a command is executed with tc:operation. After the implementation of https://issues.apache.org/jira/browse/TOBAGO-2298, the collapsible state is also processed for popups in the update model phase in order to keep the current collapsible state when the backdrop is clicked. The state is only processed if the new value is "true" in order to keep the behavior the same.
It is possible to open a box/panel/section without notifying the server. This should be changed.
If a submit is executed, the current collapsible state should always be processed in the update model phase.