I think if one has the permission to create an issue, one should also have the permission to edit title/text of an issue.
Whether only the original poster of the issue or everybody shall be able to do that might need some more thinking/discussion, but the current state of how this is dealt with is bad. E.g. someone posts an issue and it has typos, bad markup, misses markup, etc. - he can't fix it afterwards.
Thank you everyone for your input on this issue. We will take this into account and discuss possible solutions on a future update.
@vladimir -- The bitbucket issue tracker is meant to be very lightweight. We also offer JIRA, a full featured issue/project tracker with integration to Bitbucket. You can find out more information about it at http://atlassian.com/jira