On my FreeBSD 3.1-RELEASE XFree86 3.3.3
Pentium MMX +S3Virge/DX
LyX draws outside its window when I see tables.
The same effect can be seen with KLyX.
-LyX draws vertical dashed lines, it is linked with function
LyXScreen::drawVerticalTableLine in screen.C
and with GetThinOnOffLineGC in lyxdraw.C.
If I change in GetThinOnOffLineGC function variable
val.Line_style from LineOnOffDash to LineSolid this effect disappears.
But the same effect may be observed with spaces drawing (TeX objects
\quad \qquad)
With best wishes
Hisam.