Consider the following association of associations:
assoc = <|
{10,69}-><|84->1,88->2,110->1,118->4,108->1,114->8,78->2,112->1|>,
{69,84}-><|89->1,79->1,85->1,46->4,73->5,84->5,32->10,72->4,44->2,67->1,65->1,39->1,76->1,87->1|>,
{84,89}-><|77->1,69->1,32->1,46->1|>,
{89,77}-><|79->1|>,
{77,79}-><|76->1,82->8,85->5,78->4,68->1,32->1,44->2,41->4,69->1,86->2,75->1|>
{79,76}-><|79->3,76->8,89->1,68->8,65->3,78->1,69->1,73->10,85->1,83->1|>,
{76,79}-><|71->3,45->1,82->34,83->2,66->4,65->1,67->2,78->7,79->3,84->1,85->1,87->7|>,
{79,71}-><|89->3,82->2|>,
{71,89}-><|46->2,32->1|>,
{89,46}-><|10->8,34->1,41->1|>
|>
Why does Cases[Length /@ assoc // Normal, (key_List -> val_) :> key /; val == 1]
work (it returns {{89, 77}}
) while Cases[Length /@ assoc, (key_List -> val_) :> key /; val == 1]
doesn't?