Dynamic handlers with extended trait names specifying metadata aren't called on dynamically added traits

I know this is stacking a few "advanced" features on top of each other, but I've run into an issue that I think is a bug instead of expected behavior. I'm adding a trait with some metadata to an instance of a HasTraits-derived class, and then adding a dynamic notification handler that I want called when traits with that metadata change; but it never gets called. A statically defined notification handler with the same extended trait name spec gets called as expected.

A little example:

``` python

from traits.api import HasTraits, Str, on_trait_change
from traits import __version__
__version__ # --> '4.5.0'

class C(HasTraits):
a = Str(meta = True)
b = Str

@on_trait_change('+meta')
def _changed(self, name):
print "called static handler for {0}".format(name)

def handler(name):
print "called dynamic handler for {0}".format(name)

c = C()
c.add_trait("c", Str(meta = True))
c.on_trait_change(handler, "+meta")

c.a = "a" # --> called static handler for a \n called dynamic handler for a
c.b = "b" # --> nothing
c.c = "c" # --> called static handler for c
```

Is this expected behavior? Am I doing something stupid?