When you place an ingot that has been heated (like if it has just been cast or taken out of a crucible) under a mechanical press they get voided (this is on a server in v1.3)

video:
https://youtu.be/pOCh2B1R3wY

also happens in latest version (1.7)

for mechanical press recipes from create, the items do need to be cooled prior to pressing. IE Metal Presses can work on hot metals