gif transparency gone after img upload using media manager – png24 working fine.

Hey!
I have a problem.

When I upload .gif images, that have a transparent background, the transparency is set to black for all thumbnails..

If I upload a png24 file, it seems just fine…
What can be the problem here?

I read, that there was an image magick plugin, which went into the WP core some time ago.. are there any options for this?
Is there a way to check, if the hoster is missing some settings for this to work?

I am kinda clueless right now as to what I need to do.

edit: latest WP version