Not sure if it's a bug.
I'm in the process of making a new theme so I was fiddling around with 'theme options'.
I set 'Crop thumbnail height' to 100 and left 'Crop thumbnail width' empty, that way every thumbnail has a custom width depending on the original size but the height is always fixed to 100px.
I tested the gallery in various browsers and of course ie messes up everything...
This is a screenshot of the album page. See? No width.
http://i30.tinypic.com/qqbsjp.jpg
It looks ok in Firefox and others, though.
Specifying a value in 'thumbnail width' fixes the problem but, at the same time, kinda defeats the purpose because all the thumbnails will look the same.

I guess you used one of the included theme and those are designed to work with cropped thumbnails. If you want to use them, you have to make your own theme and adjust the CSS for it. I don't have the link right now, but we had a long thread about right this topic not too long ago. Should easily to be found with the forum search.

Not really. At first I thought it was a css problem with my theme too, so I switched to the ones included in the package. I tried them all and none was working in ie.
Then I set a value in 'thumb width' and ka-boom everything is working.

Just wondering, am I the only one with this problem? I've just upgraded again and same issue: http://i32.tinypic.com/331jc4x.jpg
I had a few people e-mailing me about this so I take it it's not just my computer.
If it was for me I wouldn't mind (Firefox FTW!) but, according to my stats, more than 60% of my visitors still uses IE.
Does anyone know a temporary fix?

The problem you are having is that the printImageThumb() function always puts out a width= and height= tag for the thumbnail. When you set the thumb width to empty, it outputs width="" which is being interpreted by the browser as width="0" (or something very close.)

We can fix zenphoto to omit these if the crop option is empty. That change will be in tonight's build. That should give you what you desire.