Removing @INSTALL_STRIP@ prevents stripping of debuginfo at %install time

Cleaning up top_srcdir prevents debuginfo package creation fails like this:
/usr/lib/rpm/debugedit: canonicalization unexpectedly shrank by one character

--- proftpd-1.3.2rc3/Make.rules.in	2009-01-08 16:54:26.000000000 +0000
+++ proftpd-1.3.2rc3/Make.rules.in	2009-01-08 16:54:48.000000000 +0000
@@ -29,8 +29,8 @@
 INSTALL=@INSTALL@
 INSTALL_USER=@install_user@
 INSTALL_GROUP=@install_group@
-INSTALL_BIN=$(INSTALL) @INSTALL_STRIP@ -o $(INSTALL_USER) -g $(INSTALL_GROUP) -m 0755
-INSTALL_SBIN=$(INSTALL) @INSTALL_STRIP@ -o $(INSTALL_USER) -g $(INSTALL_GROUP) -m 0755
+INSTALL_BIN=$(INSTALL) -o $(INSTALL_USER) -g $(INSTALL_GROUP) -m 0755
+INSTALL_SBIN=$(INSTALL) -o $(INSTALL_USER) -g $(INSTALL_GROUP) -m 0755
 INSTALL_MAN=$(INSTALL) -o $(INSTALL_USER) -g $(INSTALL_GROUP) -m 0644
 
 RM=rm -f
--- proftpd-1.3.2rc3/contrib/mod_load/Makefile.in	2008-09-08 21:56:02.000000000 +0100
+++ proftpd-1.3.2rc3/contrib/mod_load/Makefile.in	2009-01-08 20:37:26.000000000 +0000
@@ -1,5 +1,5 @@
 top_builddir=../..
-top_srcdir=../../
+top_srcdir=../..
 srcdir=@srcdir@
 
 include $(top_srcdir)/Make.rules
--- proftpd-1.3.2rc3/contrib/mod_wrap2/Makefile.in	2008-09-08 21:56:02.000000000 +0100
+++ proftpd-1.3.2rc3/contrib/mod_wrap2/Makefile.in	2009-07-03 17:00:41.000000000 +0100
@@ -1,5 +1,5 @@
 top_builddir=../..
-top_srcdir=../../
+top_srcdir=../..
 srcdir=@srcdir@
 
 include $(top_srcdir)/Make.rules