Hierarchical merge fail

[surli]

I just found a bug when realizing a "hierarchical" merge.
I have a list of 12 FMs representing a unique configuration, I want to merge them, but in three steps: first merging the six first, then merging the six others, and finally merging the results of the previous operations.

Sadly the final result is just a total mess, with 1920 possible configurations instead of 12...
Here the script I'm using to show the bug:

f1 = FM(widget:Name Comparison Proportion Value Discrete Dimension; Name:"Pie Chart"; Dimension:OneD;)
f2 = FM(widget:Name Comparison Proportion Value Discrete Dimension; Name:"Funnel Chart"; Dimension:OneD;)
f3 = FM(widget:Name Comparison Relationship Patterns DataOverTime Value Variations Extremum Dimension; Name:"Line Chart"; Dimension:TwoD;)
f4 = FM(widget:Name Comparison Relationship Patterns DataOverTime Value Variations Extremum Dimension; Name:"Smoothed Line Chart"; Dimension:TwoD;)
f5 = FM(widget:Name Proportion Relationship Patterns DataOverTime Value Variations Dimension; Name:"Area Chart"; Dimension:TwoD;)
f6 = FM(widget:Name Relationship Distribution Patterns Range DataOverTime Value Discrete Dimension; Name:"Ohlc Chart"; Dimension:TwoD;)

toto = merge sunion f*
a = counting toto
print "6 configurations : "
println a

r7 = FM(widget:Name Comparison Relationship Patterns DataOverTime Value Discrete Variations Dimension; Name:"Step Chart"; Dimension:TwoD;)
r8 = FM(widget:Name Comparison Relationship Patterns DataOverTime Value Discrete Extremum Dimension; Name:"Bar Chart"; Dimension:TwoD;)
r9 = FM(widget:Name Comparison Relationship Probability Distribution Patterns Range DataOverTime Value Discrete Variations Extremum Dimension; Name:"Column Chart"; Dimension:TwoD;)
r10 = FM(widget:Name Proportion Relationship Probability Distribution Patterns DataOverTime Value Discrete Variations Extremum Dimension; Name:"XY/Bubble Chart"; Dimension:ThreeD;)
r11 = FM(widget:Name Patterns Range Value Dimension; Name:"Angular Gauge"; Dimension:OneD;)
r12 = FM(widget:Name Comparison Relationship Distribution Patterns Value Discrete Extremum Dimension; Name:"Radar Chart"; Dimension:OneD;)

tata = merge sunion r*
b = counting tata
print "6 configurations : "
println b

titi = merge sunion {toto tata}
c = counting titi
print "Should have 12 configurations : "
println c