To reproduce:
- Just open the ThemeViewer and type some text in the RadDataEntry.

Workaround:
foreach (RadPanel item in radDataEntry1.Controls[0].Controls)
{
    var textBox = item.Controls[0] as RadTextBox;
    if (textBox != null)
    {
        textBox.TextBoxElement.TextBoxItem.HostedControl.MinimumSize = new Size(0, 24);
    }
}