FULL PRODUCT VERSION :
java version "9.0.1"
Java(TM) SE Runtime Environment (build 9.0.1+11)
Java HotSpot(TM) 64-Bit Server VM (build 9.0.1+11, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Windows 10

A DESCRIPTION OF THE PROBLEM :
Map<String, List<Integer>> map = new HashMap<>();
map.put("a", Arrays.asList(5, 3, 7));
map.put("b", Arrays.asList(1, 5));
map.put("c", Arrays.asList(45, 2));
map.put("d", Arrays.asList(4, 6, 2, 34));

Map<String, Integer> test = map.entrySet()
        .stream()
        .flatMap(stringListEntry -> stringListEntry.getValue().stream().map(number -> new Pair<>(stringListEntry.getKey(), number)))
         .collect(groupingBy(Pair::getKey, maxBy(comparingInt(Pair::getValue))));

The collect in the above example is unable to infer the type Pair<String Integer>. If I use a .map or other operations it is able to infer the correct type but in the collect method only "Object" is inferred.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Just use this code.
It should work, but doesn't.

Map<String, List<Integer>> map = new HashMap<>();
map.put("a", Arrays.asList(5, 3, 7));
map.put("b", Arrays.asList(1, 5));
map.put("c", Arrays.asList(45, 2));
map.put("d", Arrays.asList(4, 6, 2, 34));

Map<String, Integer> test = map.entrySet()
        .stream()
        .flatMap(stringListEntry -> stringListEntry.getValue().stream().map(number -> new Pair<>(stringListEntry.getKey(), number)))
         .collect(groupingBy(Pair::getKey, maxBy(comparingInt(Pair::getValue))));

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I expect java to infer the type Pair<String, Integer> in the collect method

The output should be a new Map with the Strings of the first map but only with the max value of each list as map value.
ACTUAL -
Java infers the type to "Object" and not as Pair<String, Integer>

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Error:(81, 25) java: incompatible types: inference variable R has incompatible bounds
    equality constraints: java.util.Map<java.lang.String,java.util.Optional<javafx.util.Pair<java.lang.String,java.lang.Integer>>>
    upper bounds: java.util.Map<java.lang.String,java.lang.Integer>,java.lang.Object

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
Map<String, List<Integer>> map = new HashMap<>();
map.put("a", Arrays.asList(5, 3, 7));
map.put("b", Arrays.asList(1, 5));
map.put("c", Arrays.asList(45, 2));
map.put("d", Arrays.asList(4, 6, 2, 34));

Map<String, Integer> test = map.entrySet()
        .stream()
        .flatMap(stringListEntry -> stringListEntry.getValue().stream().map(number -> new Pair<>(stringListEntry.getKey(), number)))
         .collect(groupingBy(Pair::getKey, maxBy(comparingInt(Pair::getValue))));
---------- END SOURCE ----------