I'm totally confused whether I need a new visa if I'll make a trip to Japan over this summer. The homepage of the US embassy tells that you may re-enter the US, insofar as your visa is still valid (mine is valid by the end of September) and "your status is 'active' in SEVIS." But my fear is: does an immigration officer at an airport really let you in when your documents expire in a few weeks? In theory s/he must, but who knows what happens to you in practice? Arbitrariness at a local DMV office is, however annoying it could be, still okay; another visit will suffice, or you may go to a different office. But that at an international airport is definitely disastrous. Who can give me an absolute confirmation about this issue?
