Collision behaviors are different if copy collision pair multiple times

[zywangppdc]

Hello,
I built a "cylinder rolling on slant board" system and copy this system 5 times, but found these 5 cylinders have different rolling behaviors. See below pic

The cylinders are all rolling down freely from top of board, and they have different behaviors e.g. the middle one runs out of board earlier than others. I want to know where this difference comes from?
I built this issue case by reusing BasicExample.cpp, see attached zip file. You can replace the same file in Bullet v2.88 source with this one, and build for issue reproduction.
P.S. I uses the preprocessor definition BT_USE_DOUBLE_PRECISION
BasicExample.zip

Thanks