Adele is right.
The underlying problem is that there are 4 actors involved in this:
- the gps has a time + timezone + DST offset [and can be assumed to be right;
- the camera has a time, but unless you can set those not a timezone / DST stamp. Older Canons have neither, in my NEX they can be set.
- OS: don't know about the others, but Windows can [and is usually set to] check the time and place through an internet connection
- LR in itself has no clock; it takes its time from the operating system
I think the problem you are seeing is in the way the OS handles DST
BTW: I don't use LR for adding gpx data to exif. I use Geosetter [which uses Exiftool]. Already used it before the Map module was added, saw no reason to change. It is an extra step, but for me it is more flexible. While the Sony allows for hour shifts, it can't handle oddball timezones like Kathmandu (UTC +5.45 IIRC).