slow validate fiailure: length001 fails in nonmoving_thr_sanity way

Reproduce with

hadrian/build test --freeze1  --docs=none --flavour=slow-validate --test-speed=slow --only="kenth001"

=====> 8800 of 9051 [9, 202, 0]
Wrong exit code for length001(nonmoving_thr_sanity)(expected 0 , actual 2 )
Stderr ( length001 ):
length001: Stack space overflow: current size 33624 bytes.
length001: Use `+RTS -Ksize -RTS' to increase it.
*** unexpected failure for length001(nonmoving_thr_sanity)