Hi,  I read this post, and I've got to say it never happened to me.
That said, I do have a 1925 Gulbransen player piano that has a crack in
the plate on the bass side.  I've never restrung this piano but I did
drill an 1/8-inch hole at the end of the crack so it wouldn't travel
any further.  I also worked on another 1925 Gulbransen that had an
identical crack, so I think there were problems in plate installations
that year.

When I rebuild a piano from the ground up, I always make sure the plate
is well seated.  Any unusual stress on a large piece of cast iron can
cause it to "explode".  This holds true for car parts, pumps, valves
and so on.  I've had one plate welded, by a very good professional
welder.  It was on a 1868 square piano.  He welded it just like our
Navy hull techs were taught -- he heated the whole plate slowly,
stabilized the temperatures then welded the broken part back in, then
incrementally lowered the temperature.  A perfect repair with no
problems; it's going on five years now, and the plate is still fine.

Dan Armstrong - Armstrong Piano Tuning & Repair
Pine River, Minnesota