Duplicate identifier question

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PowerPC603

Hi, I'm creating some custom types for my space game.

If I use this function in a module (inside a type):

Function FindCommodity:TCommodityType(CommName$)
	For Local a:TCommodityType = EachIn TCommodityType.AComm
		If a.IsWare() Then
			Local b:TWareType = TWareType(a)
			If b.Name$ = CommName$ Then Return a
		EndIf

		If a.IsWeapon() Then
			Local b:TWeaponType = TWeaponType(a)
			If b.Name$ = CommName$ Then Return a
		EndIf

		If a.IsMissile() Then
			Local b:TMissileType = TMissileType(a)
			If b.Name$ = CommName$ Then Return a
		EndIf

		If a.IsUpgrade() Then
			Local b:TUpgradeType = TUpgradeType(a)
			If b.Name$ = CommName$ Then Return a
		EndIf
	Next
End Function

It works fine.
It even compiles without errors.

But when I copy the same function into an empty bmx file and try to run it (even without extra code to call the function), using the button "Build and Run", I get an error that "b" is a duplicate identifier.
And the IDE points to line 9 ("Local b:TWeaponType = TWeaponType(a)") inside the IF-block "If a.IsWeapon()".

Does Local work differently if used in a module?