Who is unsetting this variable?

In makepp [link] I noticed an unexplicable (to me) evaporation of variable values. In Makesubs.pm we have the following closure, where $_[1] is a Makefile object and $CC is used nowhere else: my $CC; sub f_CC { $CC = $_[1]->expand_expression('find _program gcc egcc pgcc c89 cc' .