Gallery1: Thumbnails are displayed with inconsistent sizes

The following information is required to get an answer:
Get this information from the PHP diagnostic (in the configuration wizard).
Gallery URL (optional but very useful): http://www.act898.com/
Gallery version: 1.5.10
Apache version: Unknown. I use Dreamhost.
PHP version (don't just say PHP 4, please): 5.2.17
Graphics Toolkit: ImageMagick, Netpbm
Operating system: Linux
Web browser/version (if applicable): Chrome

When I upload photos to my gallery, the images are no longer resized consistently. I expected thumbnails to be resized to 150px but instead, the thumbnails seem to be displayed at the original resolution!

It is worth noting that I tested resizing from the terminal and it works correctly. I don't believe there is an issue with ImageMagick.
convert FILE -resize 150x150\> FILE

Here is a screenshot of the problem.

BAD
https://lh5.googleusercontent.com/-7PgPzoRCHOc/T70kqRsaSYI/AAAAAAABbCA/S6wRJQwCgZo/s576/ACT898%2520%2520%2520Catalog%2520%2520%2520%2520New%2520Product.png

GOOD
https://lh6.googleusercontent.com/-bcf01mx6CuA/T70kqaKP82I/AAAAAAABbB8/CI8WFiG0O8o/s576/ACT898%2520%2520%2520Catalog%2520%2520%2520%2520Sterilizer%2520Equipment%2520%2520%2520Towel%2520Warmer.png

- Tim