Shift+Enter in the formula bar starts a new line in the cell's text, as it already did while editing a cell. Enter still saves the cell. While it has focus, the formula bar grows over the grid to show every line.
Typing a line break also turns on Wrap text for the cell, so every line shows in the grid. A line break in a formula is treated as a space.
Fixed: saving from the formula bar removed the line breaks from a cell's text.