WHIZARD gets stuck in a loop when generating new events after reading in old ones

[Christian Speckner]

Occasionally, while trying to generate new events after reading in old ones, WHIZARD gets stuck in a loop searching for a valid event. Unfortunately, I have not been able to build a testcase significantly simpler than the actual input file triggering the issue, so I am quoting the full input below. Note that, while the issue seems to arise erratically, it persists once it has surfaced - cancelling the run and retrying does not help. I have looked at the code but have been unable to identify the issue.

model = SM

alias pr = u:U:d:D:c:C:s:S:b:B:g
process drellyan = pr, pr => pr, pr

sqrts = 14 TeV
beams = p, p => lhapdf {$lhapdf_file = "cteq6l.LHpdf"}

mc = 0
ms = 0
mb = 0
mZ = 91.1875 GeV
mW = 80.45 GeV
wW = 0
wZ = 0

real iae = 137.0359895
GF = sqrt (2.) * pi / iae / mW**2 / (1 - mW**2 / mZ**2) / 2

?alpha_s_is_fixed = false
?alpha_s_from_lhapdf = true
scale = (eval Pt [extract index 1 [pr]]) / 2

cuts = all Pt > 100 GeV [pr] and 
   all abs (Eta) < 2.5 [pr]

integrate (drellyan) {iterations = 5:10000, 10:10000}

histogram ptdist (100 GeV, 4 TeV) {n_bins = 40}

analysis = record ptdist (eval Pt [extract index 1 [pr]])
n_events = 1000000
?unweighted = false
simulate (drellyan) {$event_normalization = "sigma/n" checkpoint = 10000}

$out_file = "test"
write_analysis () {?out_custom = true}
!compile_analysis (ptdist) {$out_file = "test.ps"}