Dual index barcode demultiplex issue

Hello,
Following are the list of dual indexed illumina libraries we have used for illumina run.But we were not able demultiplex the data by using the barcodes.Because 99% of the data going as undetermined.

Index1 —— Index2 ( case1 )

ATGAGC —- TGAACCTT

ATTCCT —- TGAACCTT

CAAAAG —- TGAACCTT

CAACTA —- TGAACCTT

CACCGG —- TGAACCTT

There after we tried demultiplex with reverse compliment of index 2 and No changes in Index1(list are below ).This worked well and able to determine 98% of the data.The question is why the demultiplex only worked with reverse compliment of index2 and not in the case1(without reverse compliment)

Index1 —— Index2 (reverse compliment)

ATGAGC —- AAGGTTCA

ATTCCT —- AAGGTTCA

CAAAAG —- AAGGTTCA

CAACTA —- AAGGTTCA

CACCGG —- AAGGTTCA