Well, that sounds about right, vBulletin is very unstable. I bought the suite in their pre-sale back last year, when it was not even released to the public, which was strange. It must have been the worst descision I made, I certainly will not be buying vB5 when they cannot even get vB4 to a solid working product.
Since I purchased IPB, I have not had a single issue apart from me doing some stupid things with the coding, but that was easily rectified within minutes. Lately, on the vBulletin Publishing Suite the vBcms is causing major issues on many installs, again down to more bugs. It is about time they got their act together and sorted out a solid product, and stopped releasing what I would class as 'alpha' software. At the moment, vBulletin's upgrade schedules are as bad as Microsoft, if you look at the other issues as well, code left in in from vBulletin 3 (I was expecting a brand new product, not one made of two parts!!), bloated download packages (images left in from older versions), etc.
I noticed lately some of the vBulletin styling websites are failing to produce well coded styles, some of them have obvious code problems that they have introduced, while others do not even pass w3c standards.
Ah, I must of posted the link somewhere - old age getting to me..lol Yeah, I did change my username - I got tired of the old one!