Ok, here's a step-by-step explanation, detailing what's actually going on, for the people who think Hasbro want the DC character nixed:
PartiesToy manufacturer Hasbro and comic book company DC Comics
SettingEach of the two companies have created a character named "Bumblebee". One is an alien transforming robot, most often in the form of a yellow compact car or a Chevrolet Camaro in the Live Action Movies, the other is a Super Heroine, styled after a bumblebee.
ConflictOne word:
merchandising. While two characters sharing a name in-fiction even though each is owned by a different company is perfectly legal AFAIK, it's the trademarks used for marketing the goods of those two characters that pose the problem. Current trademark law does not allow the same trademarked name to be used by two different companies in the same category. For this case's sake it's mostly Toys & Sporting Goods, as well as other areas the companies are active in (someone at the trademark office must have had an off day).
PrecedentsHasbro has used the trademark in the periods 1984-1995 (not including hiatuses) and 2006-present, whereas DC comics has hardly had any toys made of the character in those time frames AFAIK. Feel free to correct me on that. The only thing worth mentioning are the Teen Titans figures made by Bandai, in the interim no less. Currently the DC character has made the top-tier character jump with plenty of merchandising in multiple toy lines to boot, while Hasbro's Bumblebee has been a favorite in every line he appeared in for the past 10 years. DC Comics Bumblebee may be older by a good number of years, and DC Comics may have applied for the trademark sooner, but precedent of use will play a factor on who eventually gets sole ownership of the name in any category.
Possible OutcomesNo matter how the case goes, it's fairly certain one of the parties will have to search for an alternative trademark for marketing the character it owns. Either one will still be named "Bumblebee", it's just the name on the toy packaging that will be different.
You know what's sad? Until now I hadn't even heard of DC's Bumblebee