I am creating a custom form for a SharePoint list using PowerApps. In a test screen, with no form, I can add a text input field (TextInput1) and a button with an OnSelect property of Reset(TextInput1). This works as expected: after typing text in the field, clicking the button returns the field to its default value ("Text Input").
However, when I use those exact same controls on a screen with an EditForm, clicking the button does nothing. The controls are both within the form (as I read is a requirement), and even on the same card. In the image below, the area with the blue fill is the form. The button in that form is identical to the button in the white area (outside the form) except that it references the text box within the form.

I have a background in software development and some experience with InfoPath and various other form-building tools, but am relatively new to PowerApps. I've tried just about everything I can find, including other reset/clear methods like setting context variables. It really seems to be related to the controls being in a form as opposed to just on a screen. Any help would be greatly appreciated!