Unresolved constraints from nested invocations are handled as follows in 18.5.2:

"If ei is a poly class instance creation expression (§15.9) or a poly method invocation expression (§15.12), C contains all the constraint formulas that would appear in the set C generated by §18.5.2 when inferring the poly expression's invocation type."

This is imprecise and may have some technical problems (to explore further and report on in the comments).