"X32:" etc. are labels, e.g. just names of functions or destinations of jump. Suppose you want to multiply A-reg by 4. Your code calls subroutine X4. That's immediately calls subroutine X2 (BSR X2), which doubles A (ADD A), and return. The return location is the next instruction of BSR X2--which is actually overlapping the subroutine X2. It doubles A again (ADD A), and returns to your code.

I think BSR here stands for "branch to subroutine", i.e. CALL.