Illustrator text wrap is very layer and group sensitive: the text-wrap causing object must be directly above the text frame for the wrap to work - your making a symbol of the text prevents that from occurring.
If you break the Symbol link whilst watching the layers palette, you will notice the symbol expands as a text frame in a group... if you then ungroup it, so that the text is sitting directly beneath the wrap-causing objects in the layer stack, the text starts wrapping as expected.
You can make a symbol in which your wrap causing objects are part of the symbol with the text, and this wraps correctly too, because by Illustrator's internal logic, the layer-order and group isolation still allows the correct relationship for text wrap to work.
I wouldn't call this a bug, in all honesty, more like a specific workflow / order of operations quirk.
Hope this helps.