In the attached file, you will find a 100 meter dash… 
…that is to say file in meter units, 100 meter line, with a standard dash linetype (5,5) applied and a linetype scale factor of 1000 to go from mm to meters.
Now, you think, hmm, the file units are supposed to be mm, not meters, I wanted a 100mm line. So, DocProperties, Units, set to mm, to the scaling question, answer No.
The line now measures 100mm long instead of 100 meters (which is what I wanted). The display hasn’t changed. All looks good. Create another line of 100mm. Apply dashed linetype to it - or use MatchProperties and match the linetype to the first line.
Hmm, the new line looks solid… 
What happened to my dash?
Save the file, close. Re-open it. Now both lines look solid… What happened?
What happened was, when the units got scaled, and I answered “No” to the “Do you want to scale” question, Rhino did not update the linetype display - which, as you note, has a 1000x scale applied to it. Now that the file is in mm, a 1000x scale will result in a solid line as the pattern length is far longer than the line length. When I create a new line, the correct scale is applied, but the original is not updated. If I close and re-open the file, the linetypes are re-applied, so the original also becomes correct.
So, what should happen in this case? Should all the linetypes in the file be scaled inversely when one changes units and does not scale the object? Or, if we leave it the way it is (probably preferable) - but then, at the very least, existing objects need to have their linetype definitions re-loaded…
–Mitch
100mDash.3dm (226.3 KB)