Batch degrades OPEN time

I shot some short 320×240 72 pixels/inch movie clips using my digital camera’s movie mode option. Apple Quicktime Pro can convert a movie into an image sequence. So I made image sequences of the movie clips and put all the images into a folder on my

Machine Model: Power Mac G5
CPU Type: PowerPC 970 (2.2)
Number Of CPUs: 2
CPU Speed: 2 GHz
L2 Cache (per CPU): 512 KB
Memory: 3.5 GB
Bus Speed: 1 GHz
Boot ROM Version: 5.1.4f0

In Adobe Photoshop CS:

I defined the following Action: Auto Level Auto Contrast Image > Adjustments > Auto Levels
Image > Adjustments > Auto Contrast
File > Save for Web

which I added to Default Actions.atn and tried to process the 17,982 .png images via

File > Automate > Batch (listing only active items) Set: Default Actions.atn
Action: Auto Level Auto Contrast
Source: Folder
Include All Subfolders
Suppress File Open Option Dialogs
Suppress Color Profile Warnings
Destination: Save and Close
Errors: Log Errors To File

with ALL History Options disabled in the History palette.

The rate for the first 1000 images was around 35 images per minute. The rate for the second 1000 images was around 29 images per minute. The rate for the third 1000 images was around 20 images per minute. … After 14,000 images the rate was around 4 or 5 per minute. The processing time for an image remained at around 1 second throughout this. What increased was the time it took to OPEN the image. Doing a RESTART of my computer didn’t improve the performance.

Doing a normal File > Open command in Adobe Photoshop CS now takes several seconds where it would take less than a second before using File > Automate > Batch.

Is there something I can do (short of reinstalling Adobe Photoshop CS) to get this degraded File > Open time back to normal?

Is there some setting that I should be using with File > Automate > Batch to avoid this degradation to occur again?

Here is the other Adobe Photoshop CS environment data (not sure why it says I have 2048 MB of memory when I really have 3584 MB):

Preferences > File Handling (listing only active items) File Save Options
Image Previews: Always Save
Icon
Macintosh Thumbnail
Windows Thumbnail
File Compatibility
Ask Before Saving Layered TIFF Files
Maximize PSD File Compatibility: Ask
Recent file list contains: 10 files

Preferences > Plug-Ins & Scratch Disks (listing only active items) Scratch Disks
First: Startup

Preferences > Memory & Image Cache (listing only active items) Cache Settings
Cache Levels: 4
Memory Usage
Available RAM: 1715 MB
Maximum Used by Photoshop: 50% = 857 MB (under 80MB, 320 MB virtual, during run)

Preferences > File Browser (listing only active items) Do Not Process Files Larger than: 200MB
Display: 10 Most Recently Used Folders in Location Popup Custom Thumbnail Size: 256 px Wide
Options
High Quality Previews
Keep Sidecar Files with Master Files

Help > System Info
Adobe Photoshop Version: 8.0 (8.0×119)
Operating System: Mac OS 10.3.9
System architecture: Unknown Processor code 313 with AltiVec Processor speed: 2000 MHz
Built-in memory: 2048 MB
Image cache levels: 4
Use image cache for histograms: No
Application folder: Macintosh HD:Applications:Adobe Photoshop CS: Photoshop scratch has async I/O enabled
Scratch volume(s):
Startup, 152.7G, 116.4G free
Primary Plug-ins folder: Macintosh HD:Applications:Adobe Photoshop CS:Plug-Ins: Additional Plug-ins folder: not set
Installed plug-ins: List was truncated when I tried to post this. The non-default ones may be AltiVecCore 8.0.0
Multiprocessor Support 8.0.1