I am in a situation where I have a green card but my wife's I-485 is still pending. She left USA when her AP was pending and later I found about this rule. I consulted some immigration attroneys and according to them, it is not a big problem.
All immigration laws about Advance parole/re-entry permit etc. are defind in 8CFR 223.1, 223.2, 223.3 and this doesn't talk any such limitation. So as per code book which every attorney refers no law has been violated. Now going to such rule, this is a travel advisory published by USCIS which was triggered by US-VISIT system. US-VISIT system was implemented in late 2003/early 2004 which focuses on both Entry and Exit procedure. If you read travel advisory it says if Person leaves country when AP is pending, he/she may be denied entry into usa and 485 may be abandoned (Read carefully word "MAY", it is not MUST).
So it all depends on case-to-case, country of citizenship for person, officer at POE and other circumstances. Bottomline is "It is not worth to take such a risk. To avoid any hassle and tension, get AP approved before you leave the country"