content in numbers invisible while typing

I was working on a spreadsheet in Numbers on my MAC and it was behaving normally where I could see everything I typed as I typed it. Then all of a sudden, my typing became invisible until I pressed enter to get out of the cell. Then everything in that cell appeared as I had typed it. I continued to work on the spreadsheet and it kept happening; my content was invisible until I got out of the cell. What happened and how can I fix it?