Question: About logarithmic integral function Li

The Li function is defined in Maple as

> FunctionAdvisor(Li, definition)
               [Li(z) = Ei(ln(z)), with no restrictions on (z)]

Special values are known

> FunctionAdvisor(Li, special_values)
Warning: when function identities information is required, only one argument -
the function name - is expected. Extra arguments are being ignored.
           [Li(0) = 0, Li(1) = -infinity, Li(infinity) = infinity]

> Li(0), Li(infinity)
                                 0, infinity
However

> Li(1)
Error, (in Li) numeric exception: division by zero

This is consistent with a computation of Ei(ln(1))=Ei(0) but,

why the Li(1)=-infinity is not in the Cache or remember table of Li ?


PS : I know I can put myself the value in the remember table

> Li(1) := -infinity
                                  -infinity
> Li(1)
                                  -infinity