
I really love the way both translator handle this 'same manga' problem. This is my experience:
Last year, I wanted to translate -beep- (its like manga but not manga), but someone else translate it first, so I reluctantly let it go, but he/she's doing a horrible job. Why? He/She direct translate it with minimum editing and not even trying to make the dialogue make sense. So I decided to translate this -beep-
I contact him/her, he/she says "yeah, you can translate it, but make sure to include my link in your blog so that the people who read there can read my blog and I will have more view as I was the first translator". As I was newbie in this translating world and stupid, I actually agreed. Stupid move. Obviously he/she didn't own that -beep- , or why the hell should I include her link in my blog, it's my translation. Thats is why I haven't post it in my blog..
How can I tell him/her that I don't want to include her link and justify myself to him/her without hurting him/her feelings? ╥﹏╥

You can't. Sorry, but you can either be honest (you'll come off as a dick to them btw) or... put the link (pretend to be nice). As a translator, I had another group pick up an ongoing project, they didn't know I was doing it, and I didn't care. Anybody can translate whatever they want, informing the other party is a courtesy, nothing more. You informed them, you owe no more than that.
Open your eyes nowww, lihuannnnnnn!!
ε=ε=(ノ≧∇≦)ノ