The -|> arrow head is not drawn when linking to <<Rect>> package containing a class.
The following example illustrates the issue:
@startuml
package p1{
}
package p2 <<Rect>>{
class c1
}
package p3{
}
p1 -> p2 : works
p1 -|> p2 : don't work
p1 -|> p3 : works
@enduml
Even if this notation do not math strict UML standard, it seems weird that this link do not work in this case.