There were some problems with this in 2.0. 25pt is a hard limit below which certain types of image can run into the problems in the text system; however, because both horizontal and vertical sliders need to have the same minimum and maximum values, there was a problem in Scrivener 2 whereby making the minimum always 25 meant that, if the image was taller than it was wide, you could end up making the height 25 and the width much smaller, causing issues.
Unfortunately, the fix for this seems to have a minor issue whereby it is now always limiting the minimum to 25 x the width/height ratio, when it should only be doing this when the image is wider than it is tall (to prevent the height from being reduced to lower than 25 points).
I have fixed this for 3.0.2.
All the best,
Keith