To reproduce: 
- Set the anchor property of RadTextBox or RadDropDownList as follows:
this.radTextBox1.Anchor = ((System.Windows.Forms.AnchorStyles)(((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Left) 
            | System.Windows.Forms.AnchorStyles.Right)));

Workaround;
Set the Autosize property to false:

this.radTextBox1.AutoSize = false;