[R] Merge failure using zoo package

[e-letter]

Data files test1, ...2, ...3, ...4 respectively.

time1,dataset1
01:01:00,0.73512097
01:01:30,0.34860813
01:02:00,0.61306418
01:02:30,0.01495898
01:03:00,0.27035612
01:03:30,0.69513898
01:04:00,0.46451758
01:04:30,0.61672569
01:05:00,0.82496122
01:05:30,0.34766154
01:06:00,0.69618714
01:06:30,0.39035214
01:07:00,0.01680143
01:07:30,0.28576967
01:08:00,0.01205416
01:08:30,0.89637254
01:09:00,0.63147653
01:09:30,0.01522139
01:10:00,0.27661960
01:10:30,0.50974124
01:11:00,0.68141977
01:11:30,0.90725854
01:12:00,0.83823443
01:12:30,0.53360241
01:13:00,0.17769196
01:13:30,0.83438616
01:14:00,0.67248807
01:14:30,0.09991933
01:15:00,0.03334966
01:15:30,0.93292355
01:16:00,0.15990837
01:16:30,0.05354050
01:17:00,0.55281203
01:17:30,0.37845690
01:18:00,0.89051365
01:18:30,0.16674292
01:19:00,0.85458626
01:19:30,0.19278550
01:20:00,0.73240405
01:20:30,0.16417524
01:21:00,0.73878212
01:21:30,0.51790118
01:22:00,0.83076438
01:22:30,0.47555504
01:23:00,0.02108640
01:23:30,0.82911053
01:24:00,0.95555646
01:24:30,0.14493657
01:25:00,0.84422332
01:25:30,0.41589974
01:26:00,0.67606367
01:26:30,0.00606434
01:27:00,0.59951991
01:27:30,0.43949260
01:28:00,0.66297385
01:28:30,0.33131298
01:29:00,0.06102041
01:29:30,0.84722118
01:30:00,0.46841491
01:30:30,0.34200755
01:31:00,0.87386578
01:31:30,0.70737403
01:32:00,0.23978781
01:32:30,0.11787278
01:33:00,0.14679814
01:33:30,0.65217063
01:34:00,0.81355908
01:34:30,0.31583482
01:35:00,0.92167666
01:35:30,0.55931271
01:36:00,0.13641271
01:36:30,0.35048575
01:37:00,0.17243584
01:37:30,0.93645686
01:38:00,0.85356548
01:38:30,0.61399352
01:39:00,0.05910707
01:39:30,0.01721605
01:40:00,0.94845557
01:40:30,0.48117810
01:41:00,0.34752402
01:41:30,0.59295472
01:42:00,0.64267429
01:42:30,0.57859933
01:43:00,0.00201441
01:43:30,0.32530995
01:44:00,0.25474645
01:44:30,0.93187534
01:45:00,0.99361033
01:45:30,0.16591641

time2,dataset2
01:01:01,0.17558467
01:01:42,0.23806514
01:02:23,0.75867726
01:03:06,0.73502357
01:03:50,0.94018206
01:04:35,0.61882643
01:05:21,0.68417492
01:06:08,0.05744461
01:06:55,0.33344394
01:07:44,0.68752593
01:08:33,0.17270469
01:09:23,0.81522124
01:10:03,0.68304352
01:10:43,0.38774082
01:11:23,0.84176890
01:12:04,0.09344446
01:12:44,0.13431965
01:13:25,0.92210721
01:14:06,0.33630635
01:14:47,0.56690294
01:15:29,0.09870816
01:16:11,0.77864105
01:16:53,0.61803441
01:17:35,0.09133728
01:18:17,0.08925487
01:19:00,0.89271117
01:19:42,0.56605742
01:20:25,0.98520534
01:21:08,0.66104843
01:21:51,0.96948589
01:22:34,0.05692690
01:23:17,0.71887456
01:24:00,0.14903741
01:24:43,0.86569445
01:25:26,0.27923513
01:26:09,0.98365033
01:26:53,0.08308399
01:27:36,0.87071027
01:28:19,0.26475705
01:29:03,0.76409811
01:29:47,0.59563256
01:30:31,0.23995054
01:31:14,0.00951054
01:31:59,0.21367270

time1,dataset1
01:02:30,0.01495898
01:03:00,0.27035612
01:03:30,0.69513898
01:04:00,0.46451758
01:04:30,0.61672569
01:05:00,0.82496122
01:05:30,0.34766154
01:06:00,0.69618714
01:06:30,0.39035214
01:07:00,0.01680143
01:07:30,0.28576967
01:08:00,0.01205416
01:08:30,0.89637254
01:09:00,0.63147653
01:09:30,0.01522139
01:10:00,0.27661960
01:10:30,0.50974124
01:11:00,0.68141977
01:11:30,0.90725854
01:12:00,0.83823443
01:12:30,0.53360241
01:13:00,0.17769196
01:13:30,0.83438616
01:14:00,0.67248807
01:14:30,0.09991933
01:15:00,0.03334966
01:15:30,0.93292355
01:16:00,0.15990837
01:16:30,0.05354050
01:17:00,0.55281203
01:17:30,0.37845690
01:18:00,0.89051365
01:18:30,0.16674292
01:19:00,0.85458626
01:19:30,0.19278550
01:20:00,0.73240405
01:20:30,0.16417524
01:21:00,0.73878212
01:21:30,0.51790118
01:22:00,0.83076438
01:22:30,0.47555504
01:23:00,0.02108640
01:23:30,0.82911053
01:24:00,0.95555646
01:24:30,0.14493657
01:25:00,0.84422332
01:25:30,0.41589974
01:26:00,0.67606367
01:26:30,0.00606434
01:27:00,0.59951991
01:27:30,0.43949260
01:28:00,0.66297385
01:28:30,0.33131298
01:29:00,0.06102041
01:29:30,0.84722118
01:30:00,0.46841491
01:30:30,0.34200755
01:31:00,0.87386578
01:31:30,0.70737403
01:32:00,0.23978781
01:32:30,0.11787278
01:33:00,0.14679814
01:33:30,0.65217063
01:34:00,0.81355908
01:34:30,0.31583482
01:35:00,0.92167666
01:35:30,0.55931271
01:36:00,0.13641271
01:36:30,0.35048575
01:37:00,0.17243584
01:37:30,0.93645686
01:38:00,0.85356548
01:38:30,0.61399352
01:39:00,0.05910707
01:39:30,0.01721605
01:40:00,0.94845557
01:40:30,0.48117810
01:41:00,0.34752402
01:41:30,0.59295472
01:42:00,0.64267429
01:42:30,0.57859933
01:43:00,0.00201441
01:43:30,0.32530995
01:44:00,0.25474645
01:44:30,0.93187534
01:45:00,0.99361033
01:45:30,0.16591641

time2,dataset2
01:03:06,0.73502357
01:03:50,0.94018206
01:04:35,0.61882643
01:05:21,0.68417492
01:06:08,0.05744461
01:06:55,0.33344394
01:07:44,0.68752593
01:08:33,0.17270469
01:09:23,0.81522124
01:10:03,0.68304352
01:10:43,0.38774082
01:11:23,0.84176890
01:12:04,0.09344446
01:12:44,0.13431965
01:13:25,0.92210721
01:14:06,0.33630635
01:14:47,0.56690294
01:15:29,0.09870816
01:16:11,0.77864105
01:16:53,0.61803441
01:17:35,0.09133728
01:18:17,0.08925487
01:19:00,0.89271117
01:19:42,0.56605742
01:20:25,0.98520534
01:21:08,0.66104843
01:21:51,0.96948589
01:22:34,0.05692690
01:23:17,0.71887456
01:24:00,0.14903741
01:24:43,0.86569445
01:25:26,0.27923513
01:26:09,0.98365033
01:26:53,0.08308399
01:27:36,0.87071027
01:28:19,0.26475705
01:29:03,0.76409811
01:29:47,0.59563256
01:30:31,0.23995054
01:31:14,0.00951054
01:31:59,0.21367270