Report the bug ASAP. If an issue persists after you've checked that you've got the latest app version + an up-to-date release for your phone, and you've deleted and reinstalled the app, report it!
I've found that after doing all of the above, if I wait for a fix it may take awhile and the problem will continue to stymy and aggravate you; why spend our time this way when we could be doing other, more productive things. Everyone assumes that someone will report the problem, or that the tech team will figure it out in their testing. This isn't always the case.
The last incarnation of the app, both my husband and I had the same problem: When opening up the reservation from the calendar (by clicking on guest's icon) and attempting to use the message icon to click through to any messages, nothing happened. This continued for almost a week (after a few days I started checking with my husband--to confirm it wasn't simply my phone mucking up). I contacted @Airbnbhelp who said they'd report the issue to the technical team. I also called Airbnb, and I think I left feedback/reported a bug (don't remember now; it's been a couple of weeks and I spend a lot of time on Airbnb either on my laptop or app--we're high-volume hosts--so stuff starts to run together). It was fixed within a day.
Hosting since Thanksgiving Day 2012 and over 1,000 stays. May you ever be the benevolent ruler of your own domain--YOUR life. Allow no other to rule over it.