A family of Microsoft word processing software products for creating web, email, and print documents.
A title is not prompt text. They're different objects with different purposes. To edit the prompt text, select the content control, then choose the Developer tab and select Design Mode. Then edit the text to the prompt that you prefer.
If you have set the option to allow carriage returns, Word will change those to soft returns instead. In this screen shot, the first line ends with a soft return, the last line with a carriage (hard) return:
If the option Allow carriage returns (multiple paragraphs) is unchecked, I am not able to duplicate your results. You might try running an Office repair to make Word behave normally.