Imported .ts files report half the true length

I have a Sagem PVR which is now in use by SWMBO, and I have the shiny new Humax.

So I pulled some .ts files off the Sagem and put them on the Humax where they play fine. Except that the reported length (in time terms) is exactly half of the true length (e.g. a film which runs for 1 hour and 10 minutes is reported as 35 minutes long). The Humax plays the files up until the true end, but the progress bar sits at 100% for the second half.

Not a big deal, but is it a known problem and is there a fix or workaround ?
You could try using AV2HDR-T2 to create the 3 files used by the box for native recording. The video/audio .ts and two more files .nts and .hmt. These contain programme content and navigation data.