Crescendo (hairpin) not reproduced accurately when going from score to part (or in reverse order).

I have been arranging a symphony for string sextet.

When I create parts from a score, all the hairpins that start at the beginning of a bar are shown in the parts as lasting through the entire bar EVEN THOUGH I modify them in the score to affect only part of the bar.

Whether I put the hairpin in the score first or into the part first the effect is the same. Either way, the length of the hairpin is not accurately shown when I go from score to part or from part to score.

This creates a great deal of extra, unnecessary and annoying work.

Please help.
Thanks.
Sincerely,
KL