One thing I like in Cacti related to how are displayed the timeframes when monitoring was down and no item values been collected. The graph for this timeframe is simply "blank" meaning no value is displayed.

For Zabbix seems the "solution" was to auto-display on graphs a line starting at beginning and ending at end of downtime timeframe, the like marking the item value.

To me this looks odd. I rather think the "blank" solution is better...