old data in results before the vote

Wen I display the results before the vote, the bars and the numbers of vote are old data, not the latest.
The chart displayed after the vote is ok, but if I check again the poll page before the vote I see the old data.
I’ve tried to clear the cache, but whit no results.
But when I see for the first time the page with another browser all is ok; then I vote and if I go to the poll page the numbers don’t change.
some hint?

thanks!

Yop Poll 5.7.5, WP 4.2.2.

https://wordpress.org/plugins/yop-poll/