Hi Companion Cube. I'm having the same issue with the spline segment and spline lines disappearing when selected. What graphic's card are you using?
My system spec:
Asus Sabertooth x79
i7 3930K cpu @ 4.5Ghz
32GB Ram
Samsung ssd 840pro 256GB x2
EVGA Geforce GTX 680 2GB (Driver 314.22)
Wacom Intuos 3
Benq 241W Monitor 1920x1200
Windows 7 Ultimate 64bit sp1