Sync problems with srt subs

Hi, my TV model is 32PFL6606D/77 (software updated, last version).

When I plug a USB or Hard Disk via USB with MKV files and SRT subs, it goes out of sync.
They're perfectly on sync on my Laptop.

Anyone can help?

Thanks.

And still not supporting Greek subtitles.
We are in 2012 but Philips is in 1912.