Ok, "not allowed" indeed is not stated, they use "rarely permitted" instead.

Quote:

Can I run more than one project at once?

We rarely permit running multiple projects at the same time, or launching a second project before fulfilling your first one. Having multiple live projects can confuse backers and split support. Running a project is a lot of work, and more than one live project will likely dilute your attention and energy. There may be exceptions out there, but that’s generally how it works. If you're a first-time creator and have multiple project ideas, we recommend selecting the one that's most developed and trying that first.


http://www.kickstarter.com/help/faq/creator+questions#faq_41837

(Assuming that each single Kickstarter entry is considered being a "project").