It is clear to me that, as sarvesheri says, it is a bug.  However, it didn´t seem quite right that the bug is not consistent: The two givens are defined in the same block. But when the main argument is an A everything goes well; when it is a LocalDate it gives an error.

Nevertheless, I have found out that the situation is not the same because class A is defined within object Ex13 and LocalDate is not.  If I modify the first code example and put class A outside object Ex13 I also get an error.  That is, if the class is defined outside the object, as LocalDate is in the first place, the given FromString is not detected.