I noticed today that after copying a paragraph from Notes to Designer (commonly done to remove embedded garbage from Word), the text object increased 1" in size and pushed the box to right where the subform ends on the right. The expand to fit was not selected. I thought this was odd that the object did not retain it's Y value.
I think this behaviour is controlled by one off the buttons in the status bar ... see image.
The last one is "Allow fixed size static text objects to grow while editing". If it has a little padlock in the bottom right corner thenthe text field will stay the same size, otherwise like in this image the text will expand to fit the content.