The base argument for intval has no effect unless the first argument is a string.

I am not sure what the best fix for this is:

We could document that you should make the first argument a string to have the base argument used.

We could convert the first argument to a string (using  convert_to_string_ex) if there is a second argument

That would mke calls made with base 10 would work as expected:
intval (1000, 11); // Returns 1331
intval ('1000', 11); // Returns 1331

However, calls using other bases might seem a bit odd:
intval ('077', 8); // returns 63
intval (077, 8); // returns 51

This would be because 077 is converted to 63, then the argument is converted to a string.

Or we could add a warning if the first arg is not a string?

Any thoughts??