I always cut the material at 90' first, then re set the saw to 45' without moving the rail and then make the angled cut. The rail needs to be clamped down...!
Steady feed rate and ensure the weight/downward pressure is on the base plate of the saw.
I think the Makita has an Anti Tip mechanism on it....?, but the Festool saws do not, so I have to keep pressure on the base plate.
All the MRMDF in the pics below was mitered at 45' using the technique I described above to create the false bulkhead.
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The finished job.....
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