Faulty bitmaps when exporting objects

I am using CoreDraw to generate vector icons which have to be "transformed" to bitmaps (Png) in different sizes (16x16, 20x20, 24x24, 32x32, 48x48,... 256x256, 512x512).

When doing so, I found three problems which I have to deal with:

1. Image sizes don't match with the pixel size in the export dialog, e.g. 16x16 may generate a 15x17 bitmap (the vector object is a square and "keep aspect ratio" is unchecked to force a 16x16 size)

2. Text is in low quality, especially the kerning is awful (the text ICON may look like  IC  O N on the exported image)

3. "Alpha Layer holes" - objects wich edges are side by side get exported with correct color values but the values for the alpha layer isn't set to opaque, so the exported image looks like a swiss cheese in certain situations.

Does anyone have seen these problems and know how to deal with them?