Ela,
 
OK, I understand your situation.  It happened to me as well twice.  Please
read further though.
 
Like belts you put around your waste (pouches/water bottle), the snap-clip
design has a center pronge in it as a guide for insertion.  It resembles a 3
pronge fork.  The two outer pronges are the springs portions of the clip
that hold it together.
 
What actually happened was that when you inserted it upside down into the
other half of the clip, the middle pronge is designed not to insert that way
and will go off the guide track in the other part of the clip, and will
slide into the area where the outer pronges are to be.  Inserting it upside
down into the other half of the clip will result in the lock you described
because one of the outer spring pronges will not be able unlock it self when
depressed because of the center pronge being beside it now.
 
What I found hard to understand is how you had to vaseline the harness off
the ferret in the first place.
 
My harnesses are 1 to 1.5 fingers slack on the bodies of the ferrets so:
  a) they can breath and swallow properly
  b) won't choke on the darn things when we're on a walk and they decide
     to stop while I'm still walking.
 
When putting a harness onto an animal, always refer to your own body and
think of a belt being put around your neck and chest....
 
Normally, my ferrets can wiggle out of their harnesses, and that's how I got
them out both times when I encountered your situation.
 
How did I resolve the snap-clip problem?  Well, when I used the pliers to
squeeze the two springy portions of the clip inwards, the center pronge
broke off.  Easy solution.  Snapped the other center pronge off while I was
at it.  Contacting Hagen was a good idea.  Perhaps if more of us send mail
or call, they'll understand it's not an isolated issue.
 
Ela, the danger in your situation wasn't from the harness design, it was
from how tightly you put the leash on.  I understand you're being upset
about the snap-clip, but there is something to be learned from this
occurance other than the harness's design.
 
When using the Hagen harness:
 
  -Determine which way you plan to put the leash on the ferret (as in
   left to right clipping or right to left)
  -Set the lengths for each part of the harness leaving at least 1 to
   1.5 fingers gap between the ferret and the harness when clipped on.
  -Always check the gap when putting the ferret into the harness. My
   ferrets have nice weight fluctuations during the 4 seasons and I have
   to make adjustments now and then.
 
   Regards,
 
   Rob, Kate and crew in Toronto, Canada
 
   (Samson, Mindy, Gabby, and Lola)
[Posted in FML issue 1635]