Does indeed seem something weird with the way of calculation. My trade was calculated like this (have to add +2 hours because of gekko runs in GMT and website with data is GMT+2)
2013-06-15 12:17:04 (INFO): ADVICE is to HOLD @ 101.940 (-0.302)
2013-06-15 12:17:04 (INFO): (PROFIT REPORT) original simulated balance: 203.171 USD
2013-06-15 12:17:04 (INFO): (PROFIT REPORT) current simulated balance: 203.171 USD
2013-06-15 12:17:04 (INFO): (PROFIT REPORT) simulated profit: 0.000 USD (0.000%)
If you look at the data around this time all trades in the last 5 minutes are above 102. The way the EMA is calculated I think mtgox gives indeed back older information if you ask for the most recent trade like you pointed out.
I'll add the next tick to do give some more data.
14:19:32 103.10297 1.48000
14:19:32 103.10296 0.14511
14:19:04 103.10295 2.00000
14:18:39 103.34000 0.25152
14:17:37 103.10295 0.17904
14:16:20 102.60000 3.55653
14:16:19 102.60105 1.17900
14:16:19 102.64001 1.57890
14:15:29 102.64000 0.36969
14:15:04 102.64000 0.02010
14:15:00 102.70000 0.61020
14:14:52 103.36535 0.75617
14:14:52 102.97000 0.25382
14:12:56 102.71000 0.02010
14:12:54 102.75000 0.95498
14:12:54 102.78000 1.21879
14:12:53 102.90252 0.00317
14:12:49 103.38000 1.00000
14:12:49 103.36535 0.01000
14:11:39 103.44000 0.25523
14:11:29 103.44000 0.76239
14:11:29 103.43210 2.56137
14:11:19 103.43210 5.43862
14:11:19 103.43200 0.10000
14:11:19 103.40000 0.79500
14:11:19 103.38150 0.01000
14:10:55 102.90252 0.20998
Edit New Tick:Didn't buy because difference not big enough.
I use
http://bitcoinwisdom.com/ for the ticker information and looks like they group their results in some way.
This might explain the difference because if you group all results you get a weighted average compared to a normal average of the latest trades.
2013-06-15 13:12:04 (INFO): ADVICE is to HOLD @ 103.103 (0.004)
2013-06-15 13:12:04 (INFO): (PROFIT REPORT) original simulated balance: 203.171 USD
2013-06-15 13:12:04 (INFO): (PROFIT REPORT) current simulated balance: 203.171 USD
2013-06-15 13:12:04 (INFO): (PROFIT REPORT) simulated profit: 0.000 USD (0.000%)
15:14:36 101.66000 0.02500
15:13:43 101.75101 0.84800
15:12:37 102.00000 5.39634
15:06:24 102.15000 24.8300
15:06:24 102.15100 4.98170
15:06:24 102.19991 0.10000
15:06:24 102.30000 0.96505
15:06:24 102.38000 4.00000
15:06:23 102.50000 0.00049
15:06:23 102.50000 46.5663
15:06:21 102.50000 42.2023
15:06:21 102.50190 0.14340
15:06:21 102.52000 0.01950
15:06:21 102.56000 11.1833
15:06:21 102.79990 0.01000
15:05:52 102.56000 0.01000
15:05:51 102.56000 0.01000