ADDITIONAL SYSTEM INFORMATION :
openjdk version "14-ea" 2020-03-17
OpenJDK Runtime Environment (build 14-ea+13-480)
OpenJDK 64-Bit Server VM (build 14-ea+13-480, mixed mode, sharing)

A DESCRIPTION OF THE PROBLEM :
The javac command recognizes JAVA_TOOL_OPTIONS has been "picked up", but it will not apply the --enable-preview .

Seen in JDK 12, 13, & 14

REGRESSION : Last worked in version 14

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
set JAVA_TOOL_OPTIONS=--enable-preview
compile a class that uses previewed features

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
javac to honor the flag it states it "picked up"
ACTUAL -
An error that mentions you need to set --enable-preview:

javac -source 14 Switch.java
Picked up JAVA_TOOL_OPTIONS: --enable-preview
Switch.java:6: error: multiple case labels are a preview feature and are disabled by default.
            case 1, 2 -> System.out.println(3);
                    ^
  (use --enable-preview to enable multiple case labels)
Switch.java:6: error: switch rules are a preview feature and are disabled by default.
            case 1, 2 -> System.out.println(3);
                      ^
  (use --enable-preview to enable switch rules)
2 errors

---------- BEGIN SOURCE ----------

public class Switch {

    public void newSwitch(int i) {
        switch (i) {
            case 1, 2 -> System.out.println(3);
            case 3 -> System.out.println(37);
            default -> System.out.println(100);
        }
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Pass the argument on the command line in addition to (or instead of) via JAVA_TOOL_OPTIONS

FREQUENCY : always