[Truffle] Error with splat args

[bjfish]

The second call to splat args results in error. Exception is caught on ArrayBuilderNode line 218.

Code:

 @a = []
 @b = 0

def splat_args( *a )
  @a.insert(@b, *a)
  puts @a.to_s
end

splat_args 60, 111
splat_args 60, 111

Error

rang.rb:4:in `splat_args': internal implementation error - ArrayStoreException null java.lang.System.arraycopy(Native Method) (RubyTruffleError)
    from rang.rb:10:in `<main>'

Expected:

[60, 111]
[60, 111, 60, 111]