Index: pym/portage.py
===================================================================
--- pym/portage.py	(revision 7746)
+++ pym/portage.py	(revision 7747)
@@ -1313,7 +1313,8 @@
 
 			# Blacklist vars that could interfere with portage internals.
 			for blacklisted in "CATEGORY", "PKGUSE", "PORTAGE_CONFIGROOT", \
-				"ROOT":
+				"ROOT", "SANDBOX_DENY", "SANDBOX_PREDICT", "SANDBOX_READ", \
+				"SANDBOX_WRITE":
 				for cfg in self.lookuplist:
 					cfg.pop(blacklisted, None)
 			del blacklisted, cfg