Horrible map reprojections

[Ben Marriage <ben(at)met.ed.ac.uk>]

Hi all,

IDL> print,!VERSION   
{ x86 linux unix 5.3 Nov 11 1999}

I'm trying to set up a particular map reprojection, and get some rather
horrible results. Can somebody try this on their machine to see if it is
reproducible please?

window,0,xs=1000,ys=300
map_set,0,180,0,limit=[-30,-180,30,180],xmar=0,$
  ymar=0,noborder=1,/grid,clip=0,/iso,/mercator
map_continents,/hires

One effect is that the reprojection does not extend all the way to the
right hand side of the plotting area (should be 0 deg long, instead it
is about -10 deg long). Another problem is this produces lines cutting
across the window (caused by the map_continents part). 

This is only part of the problem, when trying to contour some data using
a similar reprojection, I get lines cutting across the contour plot. I
thought it might be a missing data problem, so set all missing data to
!VALUES.F_NAN. No difference.

Has anybody else had a similar problem/solution?

Thanks,
Ben