If the same transformation with interpolation is applied that is currently applied on a display, it will animate the interpolation from the previous transformation rather than staying in place. Unsure if this is intended behavior based on how the previous state is saved on client.
To Reproduce
Summon a display
/summon block_display ~ ~ ~ {block_state:{Name:"stone"}}
Interpolate over 20 ticks
/data merge entity @e[type=block_display,sort=nearest,limit=1] {transformation:{translation:[0.0f,10.0f,0.0f]},start_interpolation:0,interpolation_duration:20}
Wait until interpolation completes
Apply the same transformation and interpolate again
/data merge entity @e[type=block_display,sort=nearest,limit=1] {transformation:{translation:[0.0f,10.0f,0.0f]},start_interpolation:0,interpolation_duration:20}
Notice the previous animation repeats by starting from the original default transformation instead of staying in place
Apply a slightly different transformation and interpolate again
/data merge entity @e[type=block_display,sort=nearest,limit=1] {transformation:{translation:[0.0f,0.0f,0.0f]},start_interpolation:0,interpolation_duration:20}
Notice the animation properly animates from the current transformation
Not fixed. I can't find any difference between the behaviour in pre3 and pre4.