When a type in a cell, it gets bigger?

I have a table with each cell measuring 17 pixels in height. When i begin to type in a cell, it makes the cell bigger and makes it look as if i'm typing on a second line inside that cell. When I press enter, it appears fine however i cannot use the table if this continues.

note: if i press a cell, then click on the bar at the top and THEN type, it doesn't make the cell bigger. BUT if i press a cell and begin to type, it does.