At the end of the display of the last raster line of each character line (ie. when HCC=R1 and VLC=R9), MA' captures the current value of MA.
CRTC 2 is the an exception: at the end of the display of the last raster line of the frame, MA' captures R12/R13 instead of MA.
CRTC 1 has a bug that occurs when R5 is updated with a non-zero value on specific HCC and VLC values, but only when R5 was previously 0. This disrupts the normal VMA update process, causing the CRTC to load R12/R13 into MA at the beginning of every scanline, regardless of the VCC value.