route-map NAT issue with losing connection to router

[Matt]

I configured this router to NAT based on source and destination
address. If the user is going to 1.1.1.0/26 I don't want to NAT, but
all other IPs I do want it to NAT. Here's a sample of my config (which
works fine).

!=================================================================
ip nat pool Userlan1 1.1.1.2 1.1.1.2 netmask 255.255.255.192
ip nat inside source route-map Userlan1-map pool Userlan1 overload
!
access-list 155 deny ip any 1.1.1.0 0.0.0.63
access-list 155 permit ip 192.168.3.0 0.0.0.255 any
!
route-map Userlan1-map permit 10
match ip address 155
!=================================================================

There are about 30 entries that look the same as this one--with
different subnets PATting behind different public IPs.

My problem is that whenever I add a new route-map (or delete one), I
lose my telnet connection to the router and cannot get back in until I
log in via the serial interface and delete the route map I just
created or re-create the one I just deleted (or reboot the router).
I'm not using the route maps for anything besides natting, so I can't
figure out what the heck is going on. It's a 3640 with IOS 12.0(7).
This kick-me-off behavior doesn't happen if I configure the router
from an internal interface (or from any interface on my test 3620 with
IOS 11.3).

Any info would be appreciated.