You have an interesting problem resulting from a small difference in maths.
If you look at your website in Firefox and you inspect the <li class="corners hide">
element, in the portfolio page, the height computes to be 214.933px, and in the myWork page this value computes to be 210.663px. All the other <li class="corners">
elements evaluate to a height of 210.633 on both pages. As a result, because of how floats work, the slightly taller first float forces the next float to start at its right edge instead of the edge of the parent container.
But Why?
If you look at your jpg, the dimensions are 250x261, and for the png, 250x260, 1px in height taller, that is probably the origin of the maths. All your other background images are 250x260. The maths difference results from using auto
to scale the images, a bit tricky.
How to fix it?
Try removing the extra pixel.