Block format confusing for beginner.

The Block format description does not explain if a 0x5F token is pointing to the 0x0005 byte in the windows that it repeats from that offset when it reaches 0x0000 instead of making a buffer overflow.

hd hello_test.lz4
00000000  04 22 4d 18 64 40 a7 0f  00 00 00 5f 68 65 6c 6c  |."M.d@....._hell|
00000010  6f 05 00 6a 50 68 65 6c  6c 6f 00 00 00 00 78 03  |o..jPhello....x.|
00000020  00 5b                                             |.[|
00000022

While a buffer overflow would be bad and a obvious flaw the block documentation does not explain this behaviour so I thought that you had to ramp up the repeated text in some way. (one hello turns in to three turns in to seven etc. or something like that.)