Wow, I had no idea this was such a contentious topic.
Neither did I, or I'd probably not have asked over in the original game thread. I just thought it was a slightly odd case.
I have a couple of thoughts that I think might help (and possibly, keep in mind that I'm about to argue against my own character's power curve for whatever that's worth

). Let's see if I can articulate them well enough:
First, I think it's probably a good idea to discuss the conditions of 'mundane attack' versus 'spell attack' separately, since I do think the invisibility spell tries to break out what constitutes an "attacking spell" on its own. To that end, let me tackle this real quick:
If my character cuts a rope in order to drop an anvil on a foe's head, that's the same thing as swinging a sword to hit that foe, or throwing a rock. He's using a tool to directly harm someone, and he has to make an attack roll using his own abilities/BAB/whatever.
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In the case of a trap it's a little more blurry, but to my way of thinking the distinction is still clear. Although my PC triggers the trap, once it's triggered it's no longer under his control, and any attacks made use the traps stats, not my PCs.
I do think it gets really muddy if you say 'cut the rope on your anvil' is an attack, but 'push the button on your spiked wall trap' isn't. Since, really, an anvil hanging by a rope seems like a trap to me. A really simple, obvious trap, but a trap nonetheless. I'm a little hard pressed to see something other than semantics separating the act of cutting a rope to send your enemies into the ground and cutting a rope to send a large piece of ground into your enemies. I think cutting that rope falls under the same logic that the trap does. To my mind,
for mundane attacks only, the rule seems to be: is the invisible character providing the
direct force behind the attack? Yes = invisibility goes buh-bye. Throwing rocks, knives, arrows, or swinging fists, swords, or really hard peanut brittle are all attacks. Using gravity, springs, cogs, etc which you incite by your action to in turn provide damage through another means don't. i.e., if there's a step between you and the damaging factor, you're still invisible. In the mundane world, that's enough to filter off the 'hostile energy' that makes invisibility cranky.
If we say that, I can only think of one real hair-split condition: what's the difference between cutting the rope and holding the rock in your hands when you let it drop? And even then, I think the fact that the damaging object was in direct contact with your hands prior to its assault makes for some reasonably consistent logic (for a value of logic where 'magic that gets mad when you attack' is a given).
Now, ignore all the mundane arguments when it comes to spells. Spells have / break special rules, so I think looking at them separately is probably a much safer option. And I think we can use their special rules / categorizations to draw what might be a reasonable line at least as far as this spell is concerned. Sure, a spongy fire ball that rolls around for several rounds bears a decent resemblance to, say, a summoned fire elemental. Both move against your foes and set them ablaze if you want them to.
However, Flaming Sphere isn't a Conjuration (summoning) spell. That very narrow school / subschool combo appears to have its own special 'pass' when it comes to whatever magical aggression instability is inherent in Invisibility and Vanish. It's probably safest just to say 'Conjuration (summoning) excluded' when you start the discussion, I think, for that reason.
Flaming sphere, on the other hand, is an Evocation [energy type]. We should pick something in its school to compare it to, instead, I think. I realized Call Lightning makes a good example: You cast it once, but then you can use it to move electricity about over several rounds and hurt people / damage objects. It doesn't roll about like a Flaming Sphere, but I think it's a reasonable approximation, and it's Evocation [energy type], as well. I don't think anyone would argue calling a lightning bolt in subsequent rounds is a clear attack. I think the only difference, then, is that the flaming sphere is moving horizontal instead of vertical. And without the special hall pass of a specialized school / subschool, that means it breaks your invisibility if the damage you're doing is to a creature.
Gah. I hope that made a modicum of sense.