flickering ptmultitext

if I change the foreground color for a
range of text with PtMultiTextModifyAttributes
shit happends…
when the color is changed for a range of text…
…and I type text somewhere else in the widget
everything in the textbox flashes … like in a java-applet
without double buffering … that does not happend
if I change color for some text using PED.
what have I missed??

attr.text_color = Pg_DBLUE;
PtMultiTextModifyAttributes(ABW_textarea, 5, 10, &attr, Pt_MT_FOREGROUND);