You're welcome! :)

NB: You have no guaranty at all when INSIDE the statement the increment happens, it's only guarantied AFTER the statement.

Most probably is Perl doing internal optimizations here.

Your do-block examples puzzle me, please note the difference between debugger and one-liner

  DB<1> $i=1; say for do{$i?$i:($i+1)}..$i++   #6
1


  DB<2> q

D:\Users\lanx>perl -wE "$i=1; say for do{$i?$i:($i+1)}..$i++   #6"

D:\Users\lanx>
[download]

again, unpredictable internal optimization.

If interested, you could use B::Concise to track what is happening here...

So Rule Of Thumb:

NEVER mix $i and $i++ (or --$i) inside the same statement.