I resolved the issue of icon flickering.
If you notice, the original icon has 4 repeated rectangular button designs... each one getting darker from 1 to 4. On mouse over, the icon was animated to show part 1 up to part 4.
If you plan to replace the button, just make sure that you follow the dimension of the original one... plus make 4 repeated buttons. The height dimension is the most critical... and make sure that you divide it evenly by 4.