The nether ruined portals, supposed to spawn across the surface made their way into deep caves. This might not be a bug, but to my knowledge, before 12w08a, these structures would naturally spawn either in oceans or the surface. But now, however, they can spawn like the geodes, underground, even at deep depths, as proven by the photo accompanying the report.
Linked issues
is duplicated by 16
MC-223174
Ruined Portal spawning underground
Resolved
MC-226517
The destroyed portal was generated in the caves
Resolved
MC-227818
Ruined Nether Portals Generating Underground
Resolved
MC-228594
Ruined Portal Spawn
Resolved
MC-230347
Ruined Portal genaration Underground like geodes
Resolved
11 more links
in previous versions ruined portals could spawn underground and did, though infrequently. this seems like WAI to me.