Well if you have a "big problem with it" it's not "running perfectl fine" now, is it? ;)
Some plugins don't come with their own CSS styles. It's generally up to you to style the plugin output as you see fit. That's not a shortcoming with the plugin, although the harshest among us might call it laziness on the part of the plugin author. But I'm a hands-on kinda gal myself and quite a control freak. Just add the plugin styles to your theme's stylesheet. I do it all the time.
If it really bothers you, tho, drop a note to the plugin authors and request that they add generic styles to their plugin. But bear in mind that most plugin authors labor in vain and without any recognition, much less remuneration. So that request will probably go straight to the bottom of their respective to-do lists.