Trifluralin is one of the dinitroanilines, a group of Root Inhibitors.
It appears that as germination takes place root growth (and possibly shoot growth) takes a hiding, resulting in spindly plants, barely alive, which may surface, but quickly die.
Trifluralin remains in soil largely by binding to clay particles and it is not readily removed by water draining down through soil.
My speculation – When bulbs start into growth roots will be new and may suffer to a greater or lesser extent. The bulb may be able to struggle on, using reserves before effects become noticeable, which may be in the season following. It is
this new root growth (albeit a lot stronger than a weed seedling), which may make bulbs more vulnerable than plants with consistently established roots.
Also, I wonder if it could cause a problem about the time of stem/flower formation in the bulb.
Any soil acting residual herbicide should be used with caution.
George Norris, Scotland