This is a new problem surfacing in Cubase 6 that was not in 5.5.
When no regions are selected, the Home and End shortcut keys work fine. Home goes to the first track of the sequence (Navigate - Top), and End goes to the last track of the sequence (Navigate - Bottom).
However, if any region is selected, pressing Home and End randomly cycles the selection through the regions in the project. It’s very frustrating.
(Cubase 6 32-bit mode on OSX 10.6.6 - Mac Pro 8-core)