They're notoriously overprotective. But I can't say it's not understandable.
I tried to be especially cautious about this myself. I tweaked some things (size/proportions, names, even color schemes and power sets) to differentiate the characters. Even went so far as to hire (and put on retainer) an intellectual property firm to examine everything (thanks to some push from members here actually). Better to be safe than sorry. It doesn't mean they won't still bring some kind of action against you, but at least you'll feel more secure that your case is solid against them.