I'm not 100% sure what behavior we're looking for from HS pipes, but I did some testing anyway if it helps-

Power does transmit through highspeed pipes. This includes S-curve pipes as well as Gain pipes, but not curved pipes. Power will successfully transmit to locations not on the same XYZ plane as the source without issue. Graphics issues exist- I put a pair of gain pipes back to back (leaving the Y plane and returning to it) and the laser simply passes through the empty space between them without following the curve. Also, the beam stops at the edge of an speedup HS pipe being used to slow down receiving items, though it transmits successfully through a speedup pipe at the transmission source. I didn't do complex testing on pipes potentially being used in multiple ways.

Furthermore, the laser outright disappears after a certain distance. Normally this is roughly 32 blocks, but sometimes it varies slightly.

In both the case of the laser disappearing and it not following the correct course, power still transmits successfully to the destination.

Thank you for the informations. What you confirmed is that we need to fix power routing with High speed pipes. I'm currently considering to block power transmistion over HS pipes. That would solve all the issues and would also be a good design for the HS tubes in my opinion.