This might seem like a silly thing to get upset about but...
I've been exchanging emails with a visiting scholar in my dept and I got an email from him today in which he suggested (pseudo flippantly) we co-author a paper but that it might be v controversial and not initially do my career any good.
I'm just finishing a masters and it's very different from my PhD topic so I sent a vague email asking my supervisor whether I'd have time to 'research into X topic further' but he made out he didn't really know what I meant. Despite the fact it seems him and visiting scholar were talking about me over lunch....
I kind of made out I didn't know what I meant either, because it made it v awkward and I didn't want to be humiliated if this didn't come off.
I guess I found it slightly insulting and my sup has a tendency to act in complete disbelief whenever I tell him I've been in touch with other academics!
Now I'm left feeling a bit of an idiot and don't know what to do.
Sarah

When you work for your PhD I should think you spend your time as much as possible - if not only - on stuff that will get in your PhD. Almost any PhD-student has problems in finishing his/her thesis in time. Even if it could get in your thesis, but would lead to an awkward thesis title like "A and B", I would avoid it.

i agree with adlag, only do things that will benefit your phd. because a phd is hard enough as it is!

I get that, but I have four months (not spare, MSc thesis writing) in which I feel I might get bored....
And this paper would be a major coup.

sounds like you've already decided

if you think you can handle it, then go right ahead, you know what you're capable of. i personally would want to only concentrate on my msc thesis fully and churn it out to the best of my availability, without any distractions. but if you think you can handle both, then go for it!