Okay, it seems to have been my mistake. Mobs spawned with a spawn egg named on an anvil will despawn as normal mobs, but mobs named with a name tag will not despawn. This applies to all mobs, Guardians included.
Resolution: Resolved - Works as Intended
Confirmed. Item frames use a wood texture that is darker than either the spruce or dark oak textures.
Just to be clear, I'm referring to the normal, small Guardians despawning when named. The Elder Guardians (the big ones) do not despawn under any circumstances other than Peaceful mode. I specified that this report is pertaining to regular Guardians in the first line.
Yes, the Guardians I've tested it with could not escape or kill themselves in any way; they simply despawned.
Is there any specific info I can give you to help? The bug seems pretty straightforward.
Confirmed. Additional image with the default resource pack:
http://imgur.com/0vOPAnU