actually there were bugfixes not for real hardware but rather generally for amiga display modes, in particular line drawing previously drawing beyond boundaries it was supposed to respect and fallback cpu blitting that kicked in causing unnecessary slowdowns. but it shows on real hardware the most, because winuae is faster and because hardly anyone uses amiga modes for workbench there.
i wonder if thomas richter could advise aros team on appropriate layers algorithms optimization. im particularlky reffering here to his post #21 here:
http://www.amiga.org/forums/showthread.php?t=67649&page=2
To keep it very short, besides the new functions, it is much more efficient when depth-arringing windows. V40 had an algorithm that scaled like O(n^2) in the number of overlapping windows, V45 is only O(n). Given CPU driven memory copies in some situations on rtg, this makes a noticable difference. V40 also throws fragmentation bombs at the memory system by allocating and releasing many temporary structures. V45 pools them and reuses them.
because i have an impression that aros layers lib has still similar problems.
