It's not just Inov-8s. Most of my off-road shoes wear out at the flex point on the mesh. What makes it worse is when they are constantly wet, and certain types of mud can be quite acidic - especially if mixed with animal waste. In summer I can get 400-500M out of a pair of Roclite 295s for example, but in winter that can go down to 2-300. My La Sportiva XC's started to fail in a similar place after 90M, NB MT101's he same, Mizuno Wave Harriers 180M and so on.
The thinner the upper, the quicker it will happen and the F-lite 195s are very light weight. If you want longevity, you need to keep the really light weight ones for racing and go for something like a Roclite 315 for training, whihc has a double mesh upper and is more robust.
Oddly, some (lucky) people don't have this problem at all and their shoes last almost forever. I guess it's all down to how your foot and shoe work together and where the flex point happens, and finding a shoe that works with your foot without splitting.
You shoudl definitely take it back to the retailer or manufacturer as you've done though, as without a constant stream of returns, the manufacturers won't work to improve this problem. That said, from their POV, we demand ultra lightweight shoe and they are not magicians!
A bit of careful stitching and or glueing can make them last a lot longer - I managed to eke my Sportivas out to 300 miles in the end, though it took a fair bit of gluing and re-gluing!