Remove newline at end of file and your rules will fail.
Can you attach an example failing pf.conf file?
If I understand you correctly you're saying that a ruleset which doesn't have an endline on the last line does not work.
I wouldn't consider that to be a bug.
Created attachment 209352 [details]
pf failed config
Example of not working rules.
Does your pfctl not warn about this?
On CURRENT and on 11.3 pfctl produces this error message for me:
> pf_no_endl.conf:2: syntax error
> pfctl: Syntax error in config file: pf rules not loaded
Given that I don't consider this to be a bug. That's a malformed pf.conf which the code is appropriately rejecting and warning about.