I stay in 1.86 about 2 years because when I upgreade to newer version, some torrents always can't finish the download until I switch back to 1.86.
Is newer version fix 99% problem?
My system is Centos 6 and disk format is ext4.

I don't think so, given changelogs a look there is nothing mentioned since last three updates of Tixati.

Wonder why think is less important this bug?

People make system upgrades and every time face 99% of files that were 100% before upgrading.

Even i, before I've had such a problem on Debian.