I have had dogs for a long time and have never had this happen before.  I have a 5 year old bitch that came into season about 4 weeks ago an I thought all was finished then last weekend she started bleeding again and now my boys are going mad after her and she is standing for them.  Could she have come back into season?

Sounds like she's having a split season.  One of mine did this, then went her usual time between and had normal ones after that :-)

Yes it can happen, not often and not recurring. I've been told it's due to them not ovulating the first time, so a couple of weeks or so later the cycle starts again and this time they do. No idea why, would be interesting to find out. Flipping' nuisance though especially if you have a stud on the premises :( Good luck!

It happened to one of mine, and she got pregnant in the second part of the season.

An update - Young male managed to get with her (slip mating) and last week she gave birth to 3 puppies :-)

Hope she is doing fine.  These bitches do like to catch us on the hop.  :-)

I hope it was an appropriate suitor, and that Mum and family thrive.