Created attachment 279994 [details]
On the screenshot, the column after "Location" is so narrow
that it doesn't even show its content.
This happened to me when increased the width of Location column
by only 15-20 pixels.
I think it makes more sense to give individual columns a minimum width, similar to how they already have default widths. I don't think % is the right unit for this, though, because the inspector could be very wide; pixels or em would make more sense.
Agreed on fixed width units. We don't use 'em' units much/at all in the Inspector yet.