Cisco Switching/Routing :: 3620 - Increased CPU Due To Firewall

I came across a interesting symptom. Refer to the following topology.
 
host 1 <-> R1 <-> R2 <-> FW<-> host2
 
host 1 is configured to send syslog to host2, however due to firewall ACL is not configured, this has caused a spike to 99% in R1 which already has 70% - 80% cpu.
 
My questions are :
 
1) Even if the firewall is sending RST back to host 1, it should not caused an 20% cpu increase in R1 cpu. Why this is so? Router model is 3620.

2) How do i prevent this from happening in future? This could potentially allow someone to send random traffic to hosts and cause network performance issue. Is there a way to turn off the RST response from the Firewall? This is an Cisco ASA.