Ruby rescue TypeError is not catching TypeError exception -

i'm using gem called bindata has following code block:

def assign(val)   raise argumenterror, "can't set nil value #{debug_name}" if val.nil?    unless has_parameter?(:value)     raw_val = val.respond_to?(:snapshot) ? val.snapshot : val     @value = begin                raw_val.dup              rescue typeerror                # can't dup fixnums                raw_val              end   end end 

this code meant dup object sent assign function, fixnum cannot dup'd creators put rescue block in there. have tested code multiple times in rails console , rescue works fine. however:

i, [2017-04-08t00:03:47.165387 #27899]  info -- : *** below find recent exception thrown, (but not certainly) exception made application exit abnormally *** e, [2017-04-08t00:03:47.165450 #27899] error -- : can't dup fixnum (typeerror) /home/blueserver/.rvm/gems/ruby-1.9.3-p327-turbo@symphony/gems/bindata-1.4.3/lib/bindata/base_primitive.rb:90:in `dup' /home/blueserver/.rvm/gems/ruby-1.9.3-p327-turbo@symphony/gems/bindata-1.4.3/lib/bindata/base_primitive.rb:90:in `assign' (eval):3:in `assign' 

it seems code working in catching error %99.99 of time, every once in while crashes instead. idea why rescue randomly fail? code splattered calls bindata gem, putting rescue surrounding every call tedious effort.

thanks!