I am able to reproduce the problem. From the command prompt, "help @truncate". If I browse to any of the linked functions, they are also cut off. Actually, any command help opened from the command line is chopped off, not just functions. Try "help dir".
However, I if open the help by itself and then browse to the functions, they are displayed correctly.
When I said that on my windows 8.1 x64 pc it works, I did not think to test the "help @truncate".
So, also for me, if I start help and then go to the @truncate page it works, but if I use help @truncates I see that the first lines are missing.