Dynamic Content Gallery version 3.3.5
Using jQuery JS option.
I had an issue with one of my featured images being aligned to the top instead of vertically centered, and the previous slide being visible behind the current one. I discovered that this was because the image in question had exactly the right width, but a smaller height, than the specified gallery size. My gallery size is 660 x 300 while the image is 660 x 222.
From what I can tell, the JS is assuming that if the image width matches the gallery width, then the image height must also match (or be larger than) the gallery height, and therefor it does not need to center the image. I might be wrong with this guess or with the exact logic process, but it definitely seems to be related to the width of the image. I found that if I reduced the image width by just 1 pixel, the image was properly centered and the previous slide was no longer visible.
I tried to find the section of JS code that handles this, but I'm not fluent with jQuery, and the script makes heavy use of abbreviated variable names, making it difficult for me to identify what's what.