Put differently, all those individual 1 YAC or similary small payouts you received will never ever return any PoS rewards!
Great news for people with p2pool inputs then.
Also, is this also an issue for every other PoS coin (including the original PPC) ?
Nice find! This should definitely be added to the wiki.
No. It should be
fixed.
AFAIK, No one but @sairon is working on the YAC wallet (awesome work with the coin control feature btw).
Behind adding checkpoints (on the @Windmaster fork), nothing else has been done on the client since the official release.