I have Cubase4 installed here alongside X2 Producer.
The last time I had Cubase4 installed was on my last PC...I just downloaded the 64bit version recently and tried it out.
The reason I left Cubase was because they didn't fix all the bugs in Version2 before bringing out 3.
They didn't fix all the bugs in Version3 before bringing out 4.
When they brought out Version5 without fixing the bugs in 4 I said goodbye.
All DAWs have bugs, work around them if you can, if not then jump ship.