Sorry I can't help more there. It certainly seems that way, especially when you consider the 'scope signals look clean. I'd at least put it to one side, and get another display to check it isn't a dud, otherwise there's something really fishy goin' on! At around AUD$7, they're cheap enough to have a couple spares

I like your setup, looks very compact - I certainly hadn't through about mounting on the back-side of the shield. Then again, I wanted to keep the Oak modular, and with the the pins and sockets on the shield the display wouldn't have plugged in. Very nice though!
For giggles, I reflashed the graphicstest_esp8266 sketch onto my Oak with display again, after changing two lines (10- changed Serial to Particle, 262 - removed the baud rate from begin), and this was the output I captured on OakTerm (as I was too lazy to wire up the usb serial adapter to that Oak). The Oakterm otuput is slightly easier to read, so I attached a screenshot.
[22:17:26] ILI9341 Test!
[22:17:27] Display Power Mode: 0xCE
MADCTL Mode: 0x24
Pixel Format: 0x2
Image Format: 0x0
Self Diagnostic: 0xE0
Benchmark Time (microseconds)
Screen fill 251136
Text 45268
[22:17:32] Lines 439842
[22:17:34] Horiz/Vert Lines 22091
Rectangles (outline) 15380
[22:17:35] Rectangles (filled) 521709
[22:17:36] Circles (filled) 153340
Circles (outline) 191100
Triangles (outline) 139500
[22:17:38] Triangles (filled) 217757
[22:17:44] Rounded rects (outline) 67701
Rounded rects (filled) 592739
[22:17:45] Done!