8 is a paragraph comment introducing 9..10. Therefore it is indented equally. 9 is the match of a filtering rule. 10 is the replacement, therefore an extra space is inserted to align left delimiters; which is still indentation.
Why would you refuse to distinguish between indentation and alignment even when you know what they are?.
To put it simply, you indent blocks of code, and you align symbols (such as delimiters). If it doesn't matter whether it is 2,3,4,6 or 8 spaces, then it is indentation. If it has to be exactly N spaces then it is alignment.
#indent (arbitrary distance)
while (... or
#/\ /|\ /\
#indent alignment (distance must be exactly length("while ("))
If in doubt, run Perltidy with the -i=0 option. It will still add spaces for alignment, but not for indenting.