Strange issue with TEXTOUT_P

[komame]

Can someone explain to me why sometimes the first char is not printed?
This issue occurs on both the emulator and on the real HP Prime.

Code:

EXPORT TEXTOUT_ISSUE()
BEGIN
DIMGROB_P(G1,512,40);
RECT_P();
RECT_P(G1);
//textout using width 510 at position 0,0
TEXTOUT_P("ABC / 1",G1,0,0,7,#FFFFFF,510,0); //OK
BLIT_P(G1);
WAIT(-1);
RECT_P(G1);
//textout using width 511 at position 0,0
TEXTOUT_P("ABC / 2",G1,0,0,7,#FFFFFF,511,0); //the "A" is missing
BLIT_P(G1);
WAIT(-1);
RECT_P(G1);
//textout using width 511 at position 1,1
TEXTOUT_P("ABC / 3",G1,1,1,7,#FFFFFF,511,0); //OK
BLIT_P(G1);
WAIT(-1);
RECT_P(G1);
//textout using width 511 at position -5,-5
TEXTOUT_P("ABC / 4",G1,-5,-5,7,#FFFFFF,511,0); //the "A" is missing
BLIT_P(G1);
WAIT(-1);
RECT_P(G1);
//textout using width 510 at position -5,-5
TEXTOUT_P("ABC / 5",G1,-5,-5,7,#FFFFFF,510,0); //OK
BLIT_P(G1);
WAIT(-1);
END;

EDIT:
It occurs only when the width is equal to 511 and the x-coordinate is equal or less than 0.