Test case:
def data = [
[1.0, [1.234, 0]],
]

data.each { println it }

data.each { x, y ->
println "$x $y"
}

Groovy Version: 1.1-beta-2 JVM: 1.6.0_02-b06:

[1.0, [1.234, 0]]
1.0 [1.234, 0]

Groovy Version: 1.1-beta-3 JVM: 1.6.0_01-b06

[1.0, [1.234, 0]]
Caught: groovy.lang.MissingMethodException: No signature of method: x6.doCall() is applicable for argument types: (java.util.ArrayList) values: {[1.0, [1.234, 0]]}
at x6.run(x6.groovy:7)
at x6.main(x6.groovy)