System: Windows 10 64bit
Graphic Card: nVidia GeForce 840M
Spriter Pro Ver: R5
Steps to reproduce:-
Repeat Playback: OFF
1) Create a bone and assign few sprites as child of this bone.
2) At 0ms - Change bone alpha to 0.
3) At 200ms - Change bone alpha to 100.
After step 3 you will see all the child sprites disappeared.
Note:- Toggle Repeat Playback ON/OFF before and after changing alpha or deleting key to see different kind of unexpected behaviours.