engraving question - temporary voices in vocal music

[Janek Warchoł]

Hi,

i have a SATB choral piece and occasionally some voices are split in
two. If the rhythyms differ, a polyphonic notation must be used -
that's obvious. But, what to do in the situation pictured in the
problem.png attachment? Is the notation used self-explanatory?
It's all about the first note. In my opinion it's clear that it should
be sang by both voices, but maybe an explicit polyphonic notation
should be used (see explicit.png)?
Do engraving books say anything about this?
What do you think about this?

cheers,
Janek

explicit.png
Description: PNG image

problem.png
Description: PNG image