The question is, why would savlib.dat list 1 MB in the first place? I researched this a little more and it looks like both the following is true:
1) The ROM needs only 512 kB save space
2) When running on an R4 with 1.18 or YSMenu then 1 MB is written (at least corruption takes place when the .sav file has only space for 512 kB reserved)
Proof:
Issue 1 has been said a few times now by al least 2 people here that looked at the files and 512 kB is also used by all the save hacking tools and is also confirmed by gamelists and other messages on the Internet.
Issue 2 has come up on many forums, where the data on the SD card became corrupted when using the game with an R4 and either the 1.18 kernel or YSMenu. Somebody took the trouble to create a savlib.dat file which would not have been needed when all games needed a fixed save size. There must be a reason to do that. When you Google for Pokemon Platunum and R4 then there are numerous references that on the R4 1 MB is needed (including
http://wiki.scorpei.com/index.php/R4_compatibility_list). If it is not the game that demands this size then this must be some issue that occurs on R4's (and not on other types of cards, like the Acekard R.P.G.).
So I think both are facts. The last message says it is not a bug but me not understanding something. But why on earth did somebody program a 1 MB save space in savlib.dat if not to avoid some kind of problem? And if the problem is within the R4 itself (the firmware), why does it affect 1.18 and YSMenu but not Wood R4?
Could it be that it is not in Wood R4 since it was not needed in Wood R.P.G. since the Acekard R.P.G. does not have this save issue? As established by fact 2 it is a R4 specific issue. That's the whole problem I try to raise, if the game is played on the R4 with Wood R4, will this problem occur and corrupt the FAT filesystem or will it not occur?