POSTLABELCACHE with BACKGROUNDCOLOR bug?

[Vito Meuli]

I have a problem using "POSTLABELCACHE true" in a LAYER, because it doesn't 
draw the billboard around labels anymore, which should display using the 
BACKGROUNDCOLOR directive.

I send data to the layer via an url (it works well, displaying the billboard, 
if I comment the POSTLABELCACHE directive out).

I can let the label become more evident using OUTLINECOLOR, but it's not the 
same as the BACKGROUNDCOLOR.

The layer is as follows:

LAYER # layer delle scritte fisse sulla mappa
  NAME "scritta"
  METADATA
    cliccabile "NO"
    visibilita ""
  END
  TYPE annotation
  STATUS default
  TRANSFORM false
  POSTLABELCACHE true
  CLASS
    LABEL
      COLOR 188 0 44
      #OUTLINECOLOR 255 255 255 
      BACKGROUNDCOLOR 255 255 255
      TYPE     TRUETYPE
      FONT     trebuchet_ms 
      SIZE     8
      ANTIALIAS    TRUE
      POSITION     ur
      PARTIALS     true
      BUFFER       2
      FORCE true
    END # end of label
  END
END # layer delle scritte fisse sulla mappa

I guess it is a bug. Is there any workaround?
Thank you in advance!

Vito