This evening I fixed an issue whereby the transparency was lost for the mana cost symbols when putting them on cards, giving them an ugly white square background.
A quick Google found that transparency on gif image files wasn't supported as well in 4.4 or later. I saw one solution that involved changing certain pixel colours to transparent, but that seemed like a convoluted solution that had a side effect of making too much transparent.
My solution was to just convert all the images to on png, which does handle transparency OK. Even found a way to bulk convert them which was handy :-D
