I recently expanded the size of my logical /home partition with a gparted liveCD, to do this I also expanded the primary partion my logical ones are nested in, no reformatting took place. After this something odd happened, KDE's tools (KDiskFree, Konquorer etc.) seem to think that the partition is still the same size as before. While the partitioning tools like gparted, fdisk and cfdisk seem to think it is the new size.

What exactly is happened and how do I get everything to realise it is the new size? Prefrably without reformatting

Never trust a GUI.
Have you rebooted ???.

You are not using partitions directly. Computer deals with filesystems. Partition is merely a place where you create a filesystem before you can use it. You can create a filesystem directly on the HDD without partiton table and it will work (I do it all the time).
So what happened is you enlarged the partition but did not expand the filesystem to fill it. The good news is there is resize2fs utility which can do it even with mounted filesystems, provided you run a 2.6 kernel.