PT checksum differs but sync doesn't show any difference

Hello, i’m using latest version 3.0.13 on a master slave setup with MariaDb 10.0.38 (slave) and MariaDb 10.0.31 (master) on a big dtaabase.
Some checksums are different but when i invoke pt-table-sync --verbose it doesn’t show any different record. Any ideas?
ciao
Marco