In documentation it is mentioned that “When Spreadsheet is initialized, it has the initial configuration of grid which consists of 1000 columns and 25 rows. However, when this limit runs out, additional rows and columns are rendered automatically, so you don’t need to add them.”
Actually, there are 25 columns and 1000 rows initially. When using load or parse methods to load data into spreadsheet, automatic addition of rows and columns does not work in 4.3. Also, one extra column is rendered compared to colsCount configuration option. Both works fine in 4.2. These can be verified by using the sample in configuration page and setting rowsCount to 5 and colsCount to 3.