openMSX bugs

I am seeing some display issues with SDLGL-PP renderer and odd scaling factor (simple scaler). This program should produce perfectly straight parallel lines:

10 SCREEN 7
20 FOR X=0 TO 511
30 LINE (X,0)-(X,211),(X MOD 15)+1
40 NEXT X
50 GOTO 50

But there appears an offset where lines after a certain y coordinate become 1 pixel shifted to the right.
If I set scaling factor to an even value or set renderer to SDL things look as expected.
Any hints on what am I doing wrong ?