Jan 25, 2019 01:32 AM|Ackerly Xu|LINK
It seems in your code
HTextBox.TextMode = TextBoxMode.MultiLine;
HTextBox.TextChanged += new EventHandler(control_TextChanged);
You also bind control_TextChanged to the control HTextBox with mutiple line, which causes your form to post back and trigger the event when you leave the mutipleline textbox.
By default, when you type 'Enter' key, the form will also submit and post back, so if you don't want to post back , please don't type Enter.