[kaan650]

A children binding sets Parent = nil on the children it no longer has, and on all of its children when its scope is destroyed, without checking whether they are still parented to its instance. If a child was moved to another parent in the meantime, it gets removed from there.

local header = create "TextLabel" {}
local page = source "a"

local pages = switch(page) {
    a = function() return create "Frame" { function() return header end }, 0.5 end,
    b = function() return create "Frame" { function() return header end }, 0.5 end,
}

page "b" -- header moves to page b
-- 0.5 seconds later page a is destroyed and sets header.Parent to nil

The same happens when a child is moved from one children source to another and the new one updates first, or when the scope that parented a child is destroyed after the child was moved elsewhere. This only unparents children that are still parented to the binding's instance.