Bug when computing THE with respect to TCB

!141 (merged) seems to have introduced a weird bug affecting performance when computing THE with respect to TCB.

This happens around line 916 of "instrument.py".

changed milestone to %v1.2

added bug label

created merge request !143 (merged) to address this issue

mentioned in merge request !143 (merged)

closed with merge request !143 (merged)

mentioned in commit 49744210