When casting Expansion//Explosion as the expansion side, when it makes a copy of a spell upon resolution, the resolved version of itself is still showing on the stack. This allows you to cast an instant or sorcery spell, cast a Expansion to copy that spell, cast another expansion to copy your expansion, and then when the second expansion resolves, it sees itself on the stack still to make a copy of. This interaction is an illegal game interaction as the resolved copy should not be on the stack as a target of the new copy you are making, and can cause a player to mistakenly copy the resolving spell instead of the intended target.

Casting 2 Expansion//Explosions on an instant or sorcery card while you have Ral, Storm Conduit in play is a well known combo and this interaction is not legal.

Steps to reproduce:
1) Cast any instant or sorcery spell (Spell A) that has mana value 4 or less and hold priority.
2) Cast Expansion side of Expansion//Explosion (Spell B), targeting Spell A and hold priority
3) Cast Expansion side of Expansion//Explosion (Spell C), targeting Spell B.
Resolve Spell C. Game gives the option to copy Spell A, Spell B, and itself Spell C, which has resolved.
4) Choose to copy Spell C. Game realizes the target is not legal and fizzles the spell.

Playing on iOS.

Expected Results:
1) Cast any instant or sorcery spell (Spell A) that has mana value 4 or less and hold priority.
2) Cast Expansion side of Expansion//Explosion (Spell B), targeting Spell A and hold priority.
3) Cast Expansion side of Expansion//Explosion (Spell C), targeting Spell B.
Resolve Spell C. Game gives the option to copy Spell A and Spell B.
4) Copy Spell B, resolving a new copy of Expansion, targeting Spell B.
5) Repeat.

Workaround: Don't accidentally touch Spell C to copy, it immediately fizzles the combo.

Please reference the attached screenshot and video of the interaction.