Is the mask creation broken?

[Pepi]

Hi,
I started to play with masks a bit, and I tried to do high quality mask as some of the objects were small. Have you seen the similar behaviour? Below you could see an example of this:

I created a picture with black star and then draw the mask over the star, so it looks like this:

Mask Zoom out.png (6.86 KiB) Viewed 1257 times

But when I zoom it to the picture I realised that it looks like this:

When I now tried to use the smart mask, it actually did not detected the edge at all.

And then I end to other strange:
When I draw a mask it looks like this (when I have zoom out):

Mask Draw zoom Out.png (11.91 KiB) Viewed 1257 times

Looks pretty normal for all. The mark is in middle of the mask line and all looks good.

But when I do the same on zoomed in, it looks like this:

It is not anymore in middle of the line. And actually it is as much bended than with the case of star.

Is this a common problem for all, or just on my computer?