Hello and thx for the report.
I should have seen it, alas I checked too quickly again.
Unfortunately, it's not so easy to fix, it has to do with blitter timings and bus arbitration, introduced in v3.9.1.
I thought there was a "latching delay" before the blitter started bus arbitration but that seems to be wrong. [EDIT: please see my 2nd post]
Acepower wrote: in any graphics mode, windowed, full screen, Direct3D, non Direct3D, whatever...
This kind of bug is an emulation issue, it will not be better with some video option (or I would be very surprised!