Insulated pipe not working when passing through metal tiles

What's your pipe made from? Insulated pipe isn't fully insulated, it can only reduce heat transfer.

If you need absolute insulation, use abyssalite to build your pipe.

It looks like the strange behavior for cell/building heat transfers hasn't changed since OIL/AT versions (including the part where building isolation is not part of the formula). 

Until it's adressed, the only difference for insulated piping is the mass of the building, there is no actual insulation (unlike insulated tiles). So as R9MX4 said, you'll want to use abyssalite piping (doesn't have to be insulated) for the best results.