Although in the card text Mystical Refpanel refers to what it can be chained to as a "Spell Card", the text hasn't received an errata and it doesn't say you have to activate it when a spell "card" is activated. However, the "activation" in the text seems to be speaking of the activation of effects too.

There's also a TCG ruling on wikia that says if a spell card was sent to the graveyard by Destiny hero - Diamond Dude, Refpanel can be used when that spell's effect is activated.

After that I did some testing on "World Championship 2011 Over the Nexus", which so far has had all of the correct OCG rulings, I found that my opponent (using the duel puzzle mode) could use Refpanel against the final effect of my Miracle Synchro Fusion and Pot of Duality used from the grave via Diamond Dude. Also, since at least using it in response to the Diamond Dude situation is correct, at least by TCG standards (not sure about OCG or not), I think that would mean that Refpanel can be chained to all spell "effects" that are allowed including Miracle Synchro Fusion.