I have been using Calc for two years on an iMAC. Suddenly rendering does not work properly resulting in rubbish displayed, but cell updates correct. Problem started after update to OS X 10.11.4. Same effect with Libre Office 126.96.36.199, 188.8.131.52 and 5.1.3. Same problem with large and tiny spreadsheets with no complicated content.
Input data to cell and tab to next cell sometimes produces no display of data, but data is there.
Panning and scrolling can result in cells displaying data that is not there, or displaying overplayed data.
Closing file and then opening it restores the correct display.
The problem is to do with the display of cell content, not the underlying operation of the spreadsheet data
Cal is now unusable - Help please!