Did everybody forget that they have been separate for certain periods, even after the dawn of Time?
Frames 0053 - 0074, Megan was alone, building the Caslte
Frames 0089 - 0125, Cueball was alone, building, breaking and rebuilding the Castle, though Megan was probably just off frame
Frames 0177 - 0211, Cueball was alone, building the Castle while Megan got a trebuchet
Frames 0240 - 0308, Megan was alone, building the Castle and resting a bit, while Cueball probably checked the small river
Frames 0326 - 0386, Cueball was alone, building the mini Castle
Frames 0390 - 0403, Cueball was alone, building the mini Castle, while Megan got the mini trebuchet
Frames 0419 - 0465, Megan was alone, getting and raising Poles while moving off frame every now and then
Frames 0486 - 0496, Cueball was alone, tasting the caffeinatedsemencancerbabies
Frames 0501 - 0519, Megan was alone, raising the second Planck on top of the Poles. When Cueball returns, they greet each other as if they haven't seen each other for a while
Frames 0571 - 0577, Megan was alone, finishing the bars on the top Plancks
Frames 0586 - 0628, Cueball was alone, building towers on top of the Plancks
Frames 0633 - 0636, Cueball was alone, putting flags on the towers on top of the Plancks
Frames 0729 - 0828, Megan was alone, building the top castle, sleeping, fixing the dyke (only exceptions are frames 0802 - 0805 when LaPetite stopped by, but it's generally believed that she's not Cueball in disguise)
After that, they've been pretty much together and separate less frequently.
Frames 1363 - 1375, Cueball was alone, picking berries while Megan sleeps.
Frames 1615 - 1664, Megan was alone, picking food (grapes?) and interacting with a squirpy while Cueball gets water
Frames 1925 - 1928, Cuegan was alone, sleeping, while Megan was exploring the area
Hmmm, compiling this list took a little longer than I anticipating, I even needed a lunch break halfway through