Very correct and very short. Let me spend a few more words:
RRDTool 1.3/1.4 font notification will be supported as we considered this as a bug. Full support of ALL 1.4.* features is NOT available UNTIL Cacti 0.8.8.
What are you mssing now?
I'm currently running with rrdtool 1.4.2 under 0.8.7e and it is working, I did have to manually install some of the supporting libraries for everything to run correctly. Basically once doing a ports-upgrade to the current release of everything data collection still worked but graph rendering was broken. I ended up looking through the cacti and php logs to manually install the required older versions for some of the supporting libraries.
I would not recommend trying 1.4.x as it does require a fair amount of manual installs to get it to work.