It seems the issue is dependent on how the call-back reference is obtained while registering the perl-sub. Insterestly, the callback mechanism works fine in only ONE of the callbacks I've defined and used. In several others callbacks, I get an error similar to the above post, or a "not a CODE ref" error. I cannot yet decipher what is different between how I get the references to the other subs..

They are use the "\&modname::subname" syntax & a few variants like storing the reference in a scalar and passing it later to the registration subroutine.

Note: I edited out specific strings/literals in the output below to anonymize.

SV = RV(0xae2f0ec) at 0xae2f0e0
  REFCNT = 1
  FLAGS = (PADMY,ROK)
  RV = 0xae2c0b8
    SV = PVCV(0xae0c270) at 0xae2c0b8
      REFCNT = 2
      FLAGS = ()
      COMP_STASH = 0xa1b1d30    "module-name"
      START = 0xa3324d0 ===> 0
      ROOT = 0xa3afcf0
      GVGV::GV = 0xae2f140      "module-name" :: "subname"
      FILE = "lib//module-name.pm"
      DEPTH = 0
      FLAGS = 0x0
      OUTSIDE_SEQ = 8538
      PADLIST = 0xae2c3f8
        PADNAME = 0xae2c418(0xa458a78) PAD = 0xae2c438(0xa6337a8)
             1. 0xae2c458<1> (8538,8561) "$event"
             2. 0xae2c498<1> (8538,8561) "$pdata"
             6. 0xae2c558<1> (8539,8561) "@details"
<...several other rows, one each for what seems to be a local/my varia
+ble in the subroutine...>
      OUTSIDE = 0xa19fe18 (UNIQUE)
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