Its easy to see why a set of $n$ polynomials $\{p_1\cdots p_n\}$ may have fewer than $n$ Groebner bases. For example, if $p_n=p_1*p_2+p_3$ then $\{p_1\cdots p_{n-1}\}$ and $\{p_1\cdots p_n\}$ generate the same ideal. As a result I would expect it to have $n-1$ or fewer groebner bases.
However using maple, I occasionally see systems where $n$ polynomials have more than $n$ GB. Could anyone explain why? and give a simple example?