PDF password: Acrobat vs. Indesign

Hello! This question actually goes to Adobe and perhaps someone of them replies, but others may know something as well.

In Indesign, when I export to PDF, I set a password of 5 letters length. No problem at all.

Doing the same in the sort of latest Acrobat DC (document properties window) doesn't accept 5 letters and tells me it has to have 6 at least. Setting the password via a custom action I created would accept 5 letters.

I would like to know why Acrobat handle the password length so differently.

I mean, it's my decision to use short/long or simple/complex passwords. Well, I usually set the password in the Indesign export action, but sometimes it's skipped and then Acrobat has to help. There I either use the action or the document properties.