Class of service config error

Can anyone explain the cos check-out failure I'm getting on a QFX-5100? I am also seeing this on an EX-4600.

set class-of-service interfaces et-0/0/16 unit 0 classifiers dscp test-classifier
set class-of-service interfaces et-0/0/16 unit 0 rewrite-rules dscp test-rewrite

gives this error:

test@test# commit check 
[edit interfaces]
  'et-0/0/16'
    Fixed/BA Classifier or Rewrite allowed only on  Physical interface with family inet configured
error: configuration check-out failed

et-0/0/16 is configured with inet:

set interfaces et-0/0/16 unit 0 family inet address 10.0.0.2/30

Configuring with wildcard interfaces works fine:

{master:0}[edit]
test@test# set class-of-service interfaces et-* unit 0 classifiers dscp test-classifier
{master:0}[edit]
test@test# set class-of-service interfaces et-* unit 0 rewrite-rules dscp test-rewrite  
{master:0}[edit]
test@test# commit check
configuration check succeeds
{master:0}[edit]
test@test#

Specifying individual interfaces works as expected on EX4300 and EX4200 platforms.

--Paul