Pressing enter in text frame does not automatically expand frame.
InDesign 13.1 x64
Steps to reproduce:
1. Click to drag a text frame (about 1 line high)
2. Type a number (e.g. "8")
3. Press Enter/Return
4. Type another number.
The text frame does not expand automatically in this case and [+] appears. But if you type in a phrase first instead of a number, the frame automatically expands.