#43 background images fail sometimes

[KotCzarny]

1/ start game normally, tiles are ok
2/ maximize window, tiles are scaled, some may be missing (like failed tile loading/scaling)
3/ unmaximize, tiles are ok again

so, i have two questions:
1/ what causes the bug?
2/ if i use higher resolution tiles, then after maximizing they are scaling nicely, yet they aren't scaled on initial window. can images be handled by scaling algo always, regardless of window size? that would result in nicer graphics :)