Pattern issues weird warning

Question

Take for example

head[b_[PatternSequence[_, _]]] := 9

I know this example serves no purpose as is. It also happens in useful examples such as

head[b_[_, arg : PatternSequence[_, _]]] := {arg, b}

The definition is made propely, but it issues the message

Pattern::patvar: First element in pattern Pattern[1,_] is not a valid pattern name. >>

A simpler example of the problem, suggested by @celtschk in comments

b_[PatternSequence[_, _]] :> 0

and

b_[PatternSequence[]] :> 0

Particularly interesting is an example @OleksandrR found, in which the mysterious numbering of patterns becomes more evident

(p : {a_, b_, c_})[PatternSequence[]] -> Null

Pattern::patvar: "First element in pattern Pattern[4,{Pattern[1,_],Pattern[2,_],Pattern[3,_]}] is not a valid pattern name."

Answer 1

This is a reported bug in the pattern matcher.

Answer 2

Repeated (..) command may help to solve some of the problems. I think the problem is about repeated patterns. All below examples works with no warning

head[b_[PatternSequence[_, _]]] := 9 (*err*)
head[b_[PatternSequence[_ ..]]] := 9 (*works*)

b_[PatternSequence[(_)..]]:>0

b_[PatternSequence[__ ..]] :> 0 

b_[PatternSequence[(__)..]]:>0

head[b_[_, arg : PatternSequence[_, _]]] := {arg, b} (*err*)
head[b_[_, arg : PatternSequence[_ ..]]] := {arg, b} (*works*)

EDIT 1

head[___, b_[__, arg : PatternSequence[__ ..]]] := {b, {arg}}
head[f[1, 2, 3, 4]]

outputs with no warning but trims 1 element opps!

{f, {2, 3, 4}}

EDIT 2

head9[___, b_[___, arg : PatternSequence[__]]] := {b, {arg}}
head9[f[1, 2, 3, 4]]

outputs

 {f, {1, 2, 3, 4}}