The bug

When you put multiple /execute rotated commands after each other, it will always only use the last /execute rotated command.

How to reproduce

Use the following command:

/execute rotated 0 20 rotated ~ ~20 run setblock ^ ^ ^10 stone

This doesn't set the stone block based on the rotation 0 40, which you would expect it to do because 0,20 + ~,~20 = 0,40, but instead it sets the stone block based on the rotation ~ ~20.

Note that this is inconsistent with positioned, which correctly uses context rotation, as can be observed with this command, which will place a stone block 10 blocks above 741 56 -339, and not 10 blocks above the player running the command.

/execute positioned 741 56 -339 positioned ~ ~10 ~ run setblock ~ ~ ~ stone