Working code:
    3e70:       98 81           ld      r25, Y
    3e72:       98 23           and     r25, r24 
    3e74:       e9 f3           breq    .-6             ; 0x3e70 <com_channel_buffer_forward_one+0x58>


"Optimised" code from the standard library, not working:
    3e72:       21 e0           ldi     r18, 0x01       ; 1
    3e74:       30 e0           ldi     r19, 0x00       ; 0
    3e76:       02 c0           rjmp    .+4             ; 0x3e7c <com_channel_buffer_forward_one+0x64>
    3e78:       22 0f           add     r18, r18
    3e7a:       33 1f           adc     r19, r19
    3e7c:       8a 95           dec     r24
    3e7e:       e2 f7           brpl    .-8             ; 0x3e78 <com_channel_buffer_forward_one+0x60>
    3e80:       88 81           ld      r24, Y  
    3e82:       90 e0           ldi     r25, 0x00       ; 0
    3e84:       82 23           and     r24, r18
    3e86:       93 23           and     r25, r19
    3e88:       89 2b           or      r24, r25
    3e8a:       d1 f3           breq    .-12            ; 0x3e80 <com_channel_buffer_forward_one+0x68>