lochnaes, It is a firmware issue. Following your reply I retested 3 times with 20 Albums, 15 Albums & 12 Albums. In each case when viewed Artist\Albums only 10 Albums were shown.
I tried to pinpoint what the cutoff factor was but the results were slightly different in all 3 tests.
Over the 3 tests the number of tracks viewable in those 10 folders ranged from 128 - 132, size of viewable tracks ranged from 512MB - 516MB.
In all of the tests all tracks were viewable in 9 of the 10 folders and 1 folder always displayed less tracks than it actually contained.
Which albums would not display and which folder would be short seemed to be quite random or at least did not follow the Alphabetical listing. It may have to do with the order in which the files\folders were copied to the player.
Although all this does not help the problem at least you know you are not going mad