There seems to be a bug, at least in V5.30, in applying the display priority settings to sheet views and PDF plots.
| white line set to background other color lines set to foreground | white line set to foreground other color lines set to background |
|---|
| Plan View | 
(thanks to no plan view rotation) is correct | 
is correct |
Sheet View refreshed | 
is false | 
the same as before, by chance correct |
| PDF | 
correct, by chance | 
same as before, now false |