Removed (after all unnecessary) stack pointer initialization and added explicit  switching to ROM on exit to bring back compatiblity with BASIC.SYSTEM.
diff --git a/contiki-apple2/lib/crt0.S b/contiki-apple2/lib/crt0.S
index 7d4062e..fffa3d2 100644
--- a/contiki-apple2/lib/crt0.S
+++ b/contiki-apple2/lib/crt0.S
@@ -48,12 +48,9 @@
 
 	jsr	donelib
 
-; ProDOS TechRefMan, chapter 5.2.1:
-; "System programs should set the stack pointer to $FF at the warm-start
-;  entry point."
+; Switch in ROM
 
-	ldx	#$FF
-	txs			; Re-init stack pointer
+	bit	$C082
 
 ; Back to DOS
 
@@ -64,13 +61,6 @@
 
 .segment	"BOOT"
 
-; ProDOS TechRefMan, chapter 5.2.1:
-; "For maximum interrupt efficiency, a system program should not use more
-;  than the upper 3/4 of the stack."
-
-	ldx	#$FF
-	txs	       		; Init stack pointer
-
 ; Switch to 80 column mode
 
 	.ifdef __APPLE2ENH__