When you remove all the items from the listbox on Form#1, add some items by clicking on Button1, change the text from the textbox, readd the items: it keeps the previous text from the textbox, adds the new text, then adds that string to the listbox as a new item.
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In your test/demo project: I found a bug.
When you remove all the items from the listbox on Form#1, add some items by clicking on Button1, change the text from the textbox, readd the items: it keeps the previous text from the textbox, adds the new text, then adds that string to the listbox as a new item.