I have two different galleries on my site. One runs v 1.1.5 while the other is the latest nightly build.
Same custom theme and these settings are the same for both galleries:
Crop thumbnails: checked
Crop thumbnail width: left empty
Crop thumbnail height: 100
Almost all of the original images I upload are rectangular, they're mainly tv captures and stuff like that.
My problem is, with 1.1.5 the thumbnails have an height of 100px and they're indeed rectangular, with the latest build they come up square (100x100).
Is there a way to configure the latest version so that all the thumbnails are rectangular as they used to be in 1.1.5?

I don't understand exactly. If you want uncropped images you should not check the crop thumbnails options. Also if you check cropping you should set a width and a height.

Basically I would like all the thumbs to have the same height with the width changing accordingly. Like this http://i44.tinypic.com/nxosi8.jpg
Landscapes are wider, portraits are narrower but the thumbnails have all the same height.
I found out in 1.1.5 that leaving the width field blank that would do the trick but now I can no longer reproduce that.

[EDIT - Disregard]
I know there's printCustomAlbumThumbMaxSpace but since the width of each pic is different I can't set a specific width. And if I don't set a width the function won't work.
Also, I don't know if I'm using it wrong but it only works for the album thumbnail and not for all the thumbnails inside the album. (the ones beetween <?php while (next_image(false, $firstPageImages)): ?> and <?php endwhile; ?> so we are clear) It just prints the first image inside over and over.

[EDIT 2]Ok, nevermind.
So now the question is: are the max space functions the right way to accomplish what I am after?
I set the height argument to 100 and put a big number for width.
<?php printCustomAlbumThumbMaxSpace('',800,100,null,null,true); ?>
<?php printCustomSizedImageThumbMaxSpace('',800,100,null,null,true); ?>

You want the printCustomAlbumThumbImage() function. Pass NULL for the size and width and 100 for the height.

Thanks sbillard. It's working for the album thumb but not for the thumbs inside each album. Is there another function for that?

No, but the album page is a different script from the index page. You would have to change both index.php and album.php.

Same problem again. How can I achieve this with printLatestImages?
The default thumb size is 85x85. If I override the default function, pass NULL for width and 100 for height the image is displayed full size.

printLatestAlbums() or more specific the image_album_statistics plugin does not support the "maxspace" way. Only cropped thumbs or uncropped images are possible.