Hola Jorge,
no, this looks unfortunate, but is not really a bug.
DiracTrace does not evaluate the trace.
But Tr[constant] gives 4*constant.
So what you are calculating is tr( tr( g_a g_b) ) which is
16 g_{a,b}
So, to just calculate a trace do:
TR[GA[a,b]]
or
Tr[GA[a,b]]
Rolf Mertig
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