Something weird is happening in the host mir server. With the external display:

[1452530027.692778] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=122µs
[1452530027.696227] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=213µs
[1452530027.721833] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=122µs
[1452530027.738162] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=122µs
[1452530027.746433] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=122µs
[1452530027.767614] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=152µs
[1452530027.788246] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=152µs
[1452530027.802712] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=3326µs
[1452530027.819254] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=1800µs
[1452530027.823222] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=122µs
[1452530027.832897] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=122µs
[1452530027.838909] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=2807µs
[1452530027.855970] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=122µs
[1452530027.870468] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=2289µs
[1452530027.889451] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=1709µs
[1452530027.907306] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=2868µs
[1452530027.913562] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=213µs
[1452530027.934255] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=152µs
[1452530027.947898] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=518µs
[1452530027.960167] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=1495µs
[1452530027.969903] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=183µs
[1452530027.989436] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=122µs
[1452530027.996852] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=122µs
[1452530028.006070] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=152µs
[1452530028.018766] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=152µs
[1452530028.034850] frontend::MessageProcessor: mediator=0xb138413c: submit_buffer(), elapsed=152µs

Note the intermittent long (over 10 times) posts.

Without the external display:

[1452530459.993648] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=122µs
[1452530460.010556] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=122µs
[1452530460.027098] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=122µs
[1452530460.044067] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=213µs
[1452530460.060823] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=213µs
[1452530460.078952] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=305µs
[1452530460.098607] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=335µs
[1452530460.115149] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=335µs
[1452530460.133431] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=610µs
[1452530460.147806] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=366µs
[1452530460.162456] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=793µs
[1452530460.181531] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=579µs
[1452530460.198073] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=366µs
[1452530460.213425] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=671µs
[1452530460.231340] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=335µs
[1452530460.247150] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=366µs
[1452530460.265798] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=366µs
[1452530460.280753] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=335µs
[1452530460.298119] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=366µs
[1452530460.314417] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=335µs
[1452530460.332302] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=671µs
[1452530460.341519] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=91µs
[1452530460.358732] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=152µs
[1452530460.374908] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=122µs
[1452530460.392488] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=122µs
[1452530460.408633] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=122µs
[1452530460.425145] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=244µs
[1452530460.440985] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=91µs
[1452530460.459297] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=122µs
[1452530460.475320] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=122µs
[1452530460.491740] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=122µs
[1452530460.509015] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=213µs
[1452530460.525221] frontend::MessageProcessor: mediator=0xaf8030d4: submit_buffer(), elapsed=213µs