This is only happen if:
A. Trim is enable
B. Item Playback-rate is lower than 1
C. You make something of the split item only hidden from left edge before splitting
And if A+B+C is true the result would be as follow.
% size of empty area at right side of left item
= hidden area size*(1 - item playback rate)
It is one of the meanwhile, personally think, rather rare very old -
little errors, under hood bugs or whatever
4 beats hidden from left edge, item play rate 0.5 = right side empty area at left item 2 beats
4 beats hidden from left edge, item play rate 0.25 = right side empty area 3 beats
This is not happen if trim is not enable
or you make something not only hidden from
left edge before splitting
or item playback rate is higher 1
or split the hidden area from item before split the other
or at least glue the item before splitting..
The biggest problem for getting into this behavior is hiding only an area from left edge.
Of course it is an open bug.. but with the possibility to easy avoid.