When creating graphs, Zabbix has a tendency to concatenate values to decimals (like 1500 which would become 1.5k). Certain units ('%', 'ms' and 'rpm') are blacklisted from this and thus always have their numbers displayed in full. These units are set on line 441 in include/func.inc.php in my Debian packaged version of Zabbix 1.8.5:

// black list wich do not require units metrics..
$blackList = array('%','ms','rpm');

My suggestion is to make this array configurable, so that people can add their own units which they wish to have displayed only in full numbers. (In my particular case, I track the number of licenses for a certain product and have labelled this unit 'lic'. I need to see the exact count of licenses on the graphs to be able to see how many were added in a certain time period ...)