Hi again,
I ripped a DVD with the IFO/BUP bug and got some 'Pack Header Not Found' warnings from dvddecrypter:
I 10:43:09 Operation Started!
I 10:43:09 Source Device: [0:1:0] IDE DVD-ROM 16X 2.02 (Z

I 10:43:09 Source Media Region Code: 1, 2, 3, 4, 5, 6, 7, 8
I 10:43:09 Source Copyright Protection System Type: None
I 10:43:09 Destination File: E:\DVD.ISO
I 10:43:09 File Splitting: Auto
I 10:43:09 Detect Mastering Errors: No
I 10:43:09 Remove Macrovision Protection: Yes
I 10:43:09 Extracting Sectors... (LBA: 0 - 2271599)
I 10:43:10 Found VOB File: VTS_04_0.VOB - (LBA: 261 - 261) - KEY: N/A
I 10:43:10 Found VOB File: VTS_03_0.VOB - (LBA: 261 - 261) - KEY: N/A
I 10:43:10 Found VOB File: VTS_02_0.VOB - (LBA: 261 - 261) - KEY: N/A
W 10:43:10 Sector 261 - Pack Header Not Found (0x00010200)
W 10:43:10 Sector 262 - Pack Header Not Found (0x08000200)
W 10:43:10 Sector 263 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 264 - Pack Header Not Found (0x01010200)
W 10:43:10 Sector 265 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 266 - Pack Header Not Found (0x01010200)
W 10:43:10 Sector 267 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 268 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 269 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 270 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 271 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 272 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 273 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 274 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 275 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 276 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 277 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 278 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 279 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 280 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 281 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 282 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 283 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 284 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 285 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 286 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 287 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 288 - Pack Header Not Found (0x05010200)
W 10:43:10 Sector 289 - Pack Header Not Found (0x05010200)
I 10:43:10 Found IFO File: VIDEO_TS.IFO - (LBA: 290 - 296)
I 10:43:10 Found VOB File: VIDEO_TS.VOB - (LBA: 297 - 336) - KEY: N/A
I 10:43:10 Found BUP File: VIDEO_TS.BUP - (LBA: 337 - 343)
I 10:43:10 Found IFO File: VTS_01_0.IFO - (LBA: 344 - 410)
I 10:43:10 Found VOB File: VTS_01_0.VOB - (LBA: 411 - 95800) - KEY: N/A
I 10:44:15 Found VOB File: VTS_01_1.VOB - (LBA: 95801 - 620087) - KEY: N/A
I 10:49:02 Found VOB File: VTS_01_2.VOB - (LBA: 620088 - 1144374) - KEY: N/A
I 10:52:46 Found VOB File: VTS_01_3.VOB - (LBA: 1144375 - 1668661) - KEY: N/A
I 10:55:56 Found VOB File: VTS_01_4.VOB - (LBA: 1668662 - 2192948) - KEY: N/A
I 10:58:43 Found VOB File: VTS_01_5.VOB - (LBA: 2192949 - 2271201) - KEY: N/A
I 10:59:07 Found BUP File: VTS_01_0.BUP - (LBA: 2271202 - 2271268)
I 10:59:07 Found IFO File: VTS_02_0.IFO - (LBA: 2271269 - 2271275)
I 10:59:07 Found VOB File: VTS_02_1.VOB - (LBA: 2271276 - 2271280) - KEY: N/A
I 10:59:07 Found BUP File: VTS_02_0.BUP - (LBA: 2271281 - 2271287)
I 10:59:07 Found IFO File: VTS_03_0.IFO - (LBA: 2271288 - 2271294)
I 10:59:07 Found VOB File: VTS_03_1.VOB - (LBA: 2271295 - 2271304) - KEY: N/A
I 10:59:07 Found BUP File: VTS_03_0.BUP - (LBA: 2271305 - 2271311)
I 10:59:07 Found IFO File: VTS_04_0.IFO - (LBA: 2271312 - 2271318)
I 10:59:07 Found VOB File: VTS_04_1.VOB - (LBA: 2271319 - 2271323) - KEY: N/A
I 10:59:07 Found BUP File: VTS_04_0.BUP - (LBA: 2271324 - 2271330)
I 10:59:07 Operation Successfully Completed! - Duration: 00:15:58
I 10:59:07 Average Read Rate: 4.742 KB/s (3.4x) - Maximum Read Rate: 6.867 KB/s (5.0x)
After I copied the IFO's to the BUP files, I tried to burn the DVD with Nero again. I got a warning again: "DVD-Video files reallocation failed. The resulting DVD-Video might be unplayable. Do you want to continue?"