Definitely check with collaborators prior to presenting unpublished work which you are all working on trying to publish together. In other words, a formal collaboration with intent to publish a joint paper, or intent to present at a symposium or seminar, pretty much states that you are working together. You don't want to appear ungracious or try to "scoop" credit.
In medicine, there is also the problem that journals do not want to accept "previously published" work, and some journals define presenting at conferences as prior publication, whereas other journals (Journal of the American Medical Association) state specifically that presenting at a symposium, even if they publish conference proceedings, does not disqualify work from being submitted for publication.
JAMA and the New England Journal of Medicine also place an embargo on works submitted for publication. They specifically do not want articles which are currently under review by referees to be leaked or announced to the media. I don't think that sort of marketing hoopla is as common in mathematics.
But, in my opinion, common courtesy certainly dictates that collaboration on research implies a joint duty to decide together where to submit for publication and where to present the research. If there are arguments about where, when, how, and how much to present of whatever you are working on, that is more about the ability to collaborate and peacefully negotiate decisions, and more of a personality matter.