For those that wonder how the heck you even can dereference a qr// object: I'm sorry, I don't know either. :)

But this below is usually how I go about when I find an unexpected behaviour of this kind. I perhaps won't get all the whys, but I might get an explanation that works for me and that will add another piece to the puzzle.

I do believe that perl interally treats a qr// as a blessed scalar, being blessed into class Regexp. The object itself is as magical as objects get I think, and we can't get any useful info out of just printing the object as you usually can, but overload can help us out:

  use overload;
  print overload::StrVal(qr/asdf/);
  # Regexp=SCALAR(...)
[download]

And Devel::Peek help us in another way:

  use Devel::Peek;
  Dump(qr/asdf/);
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yielding:

SV = RV(0x1af1fd8) at 0x1b0f118
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,ROK)
  RV = 0x1b0f190
  SV = PVMG(0x1c2c5ac) at 0x1b0f190
    REFCNT = 1
    FLAGS = (OBJECT,RMG)
    IV = 0
    NV = 0
    PV = 0
    MAGIC = 0x1af012c
      MG_VIRTUAL = 0x2808c138
      MG_TYPE = 'r'
      MG_OBJ = 0x1b0b51c
    STASH = 0x1de7570   "Regexp"
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showing us that regexes are magical. I don't see it being defined anywhere. But I have no idea why this is the case. But I can't say I'd expect a sane dereference value for a magical object. :) In fact, thinking about it I'd more expect undef than anything else because... the value isn't defined since it's not actually a scalar, and what would be a good substitute value anyway?

Hoped this helped in some way,
ihb