Morph menu -> 'stack of cards' -> 'become stack of cards' does not work. For testing I used six TextMorphs three labels and three fields. Morphs used as labels have 'shared' prefix in their Morph names. Attached is zipped morph file produced with Squeak v3.8.1. Both that and v6.0 can open this thile as a morph. Open it as a morph and try clicking 'Next' and 'Previous' in both versions. v3.8.1 works ok, v.6.0, does not.

my StackMorph [Squeak 3.8.1].morph.zip

Stack morph tutorial: https://wiki.squeak.org/squeak/2720