Solid Tantalum
capacitors have the failure mode he is observing, they short.
Many electronics companies banned their engineers from designing them in for
this exact reason. When they short, they BURN UP, often taking large chunks
of the circuit board with them.
In 1984 or 1985, we had a 10uF tantalum cap blow on a COMBOARD at a
customer site. It put a 6mm hole in a six layer board and took out
the boards on either side of it in the BA-11 box.
I saw the board when it was returned - looked like someone shot it
with a .22 at close range.
Plus I'll bet the smell was pretty interesting.
Peace... Sridhar