|Looking at the source code[^], the
UCTextBoxEx is a user control which wraps a
TextBoxEx instance raises its
TextChanged event, the parent
UCTextBoxEx instance raises its own
TextChanged event. But it passes the original
sender through unchanged, which means the sender is the wrapped
TextBoxEx instance, not the
This feels like a bug in the library, but there might be a reason for it. You could try reporting an issue[^], but bear in mind the author is Chinese and claims to have poor English.
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