Ignored error during build in src/preproc/refer

[Thomas Klausner <wiz%NetBSD.org@localhost>]

During a -current build on amd64 I get:

mkdir src/preproc/refer
c++ -I. -I/usr/src/gnu/dist/groff/src/preproc/refer  
-I/usr/src/tools/groff/obj.amd64/build/src/include 
-I/usr/src/tools/groff/../../gnu/dist/groff/src/include -DHAVE_CONFIG_H -O 
-I/usr/src/tools/compat/obj.amd64 -I/usr/src/tools/compat/obj.amd64/include  
-I/usr/src/tools/groff/../compat -DHAVE_NBTOOL_CONFIG_H=1  
-D_FILE_OFFSET_BITS=64 -c  /usr/src/gnu/dist/groff/src/preproc/refer/command.cpp
if test -n ""; then  /build/tools/bin/nbyacc -v -d 
/usr/src/gnu/dist/groff/src/preproc/refer/label.y;  else  
/build/tools/bin/nbyacc -v /usr/src/gnu/dist/groff/src/preproc/refer/label.y;
fi
test -f y.tab.h && mv y.tab.h y_tab.h

*** Failed target:  label.cpp
*** Failed command: test -f y.tab.h && mv y.tab.h y_tab.h
*** Error code 1 (ignored)

Is there a bug in the Makefile?
 Thomas