Potty training our miniature schauzzer

Question
Our 2 mini-schnauzers are 4 months old and have recently started pooping in their shared kennel.  The kennel is fairly small.  They eat only in the evenings but still have accidents the next day.  They go out twice in the evenings (usually for 10-15 minutes)and for almost an hour in mornings before work.  For about 2 months they had no accidents during the 8-9 hour day while we are gone.  When playing with us in the evenings, the dogs have no trouble ringing a bell at the door to let us know he or she wants out.  Any suggestions?  Less food?  Separate kennels?
Thank you so much.

Answer
Ok.  This is strange because they never used to do this.  hmmm. You could try separate kennels and see who it is that is pooping.  How did you toilet train them? It may be a case of going back to square one with the toilet training.  I need a wee bit more info on the setting.  Is the kennel outside? Is it a run or just an enclosed kennel?  Is it dry food or meat you feed them?  For some reason your dogs have come to the conclusion that it's OK to poop there. Whether the first time was an accident, and then because there was no repercussion assumed it was fine.