Hey anyone found that sometimes when there are too many files/folders exist in the sidebar,
when you move your mouse into/out the sidebar area, the line height( maybe margin, maybe padding ) of the file/folder names change.
Is it a design on purpose?
if it is, is there a way to turn this function off?
if not, is there a tip to (permanently) avoid that behavior?
In addition, this behavior doesn’t occur when the scroll-bar of the sidebar is at the top.
Yes, I see this a lot too. I mentioned it a while back and Jon said it was because the side bar doesn’t support headings and entries using different font sizes. I don’t think I have that going on, and have been meaning to test it again, but always find some more important programming to be done first. 
In any case, I’m glad you mentioned it. Hopefully it will get some some traction.
I’m using the default theme with sidebar customized by myself.
Adjusted the font size and font face, and some other stuff…
Will it be solved by having all the font size the same?
I work with a lot of files open at once and see this line-height change regularly. It doesn’t bother me too much and I figure that, Jon, will get around to fixing it eventually.
Default theme.