I am trying to use urca library to do cointegration test, and its function ca.jo, which conducts the Johansen procedure on a given data set.

I think a lag order of 1 is possible for a cointegrated VECM, which means it does not have short term error correction. For example, we have VAR(1)

$$
X\_t=\Pi\_1X\_{t-1} + \epsilon\_t
$$
and its VECM is 
$$
\Delta X\_t = \Pi X\_{t-1} + \epsilon\_t
$$
where $\Pi=\Pi\_1-I\_2$

Why does ca.jo specify the minimum lag order to be 2? Is there a reason behind it?