I hit a mirror failure on my general mirror branch testing and confirmed it reproduces on current develop with the mirror branch merged. The config has 5 tables, 3 of which are mirrors.
The noteworthy thing is that all mirrors are row-store.
The failure is:
mirror: 10651/10651 mismatch: table:T00001: {0000010651.00/opqrstuvwxyzabcdefghij}/{0000010651/EMNOPQRSTUVWXYZABCDE----azyxwvuts}, table:T00002: {0000010651.00/opqrstuvwxyzabc}/{0000010651/rMNOPQRSTUVWXYZABCDEFGH} last successful match was 10650 mirror error: base cursor (table 1): dumping to WT_TEST.4/FAIL.pagedump.1 mirror error: table cursor (table 2): dumping to WT_TEST.4/FAIL.pagedump.2 mirror error: base key number 10651 in table 3: dumping to WT_TEST.4/FAIL.pagedump.3 mirror: 10684/10684 mismatch: table:T00001: {0000010684.00/opqrstuvwxyzabcdefghijklmnopqrstu}/{0000010684/GMNOPQRSTUV}, table:T00002: {0000010684.00/opqrstuvwxyzabc}/{00000106} last successful match was 10683 mirror: 10804/10804 mismatch: table:T00001: {0000010804.00/opqrstuvwxyzabcdefghijklmnopq}/{0000010804/AMNOPQRSTUVWX}, table:T00002: {0000010804.00/opqrstuvwxyzabc}/{0000010804/AMNOPQRSTUgfrqponmlkxwv--onmlk} last successful match was 10803 mirror: 10957/10957 mismatch: table:T00001: {0000010957.00/opqrstuvwxyzabcdefghi}/{0000010957/pMNOPQRSTUVWXYZABCDEFGHIJKLM}, table:T00002: {0000010957.00/opqrstuvwxyzabc}/{0000010957/pMNOPQRSTUnmlkjinmlemBCDEFGHlkJKvutsr} last successful match was 10956 mirror: 11021/11021 mismatch: table:T00001: {0000011021.00/opqrstuvwxyzabcdefghijklmnopqrstuv}/{0000011021/QMNOPQRSTUVWXYZA-zyxwvuts--rqponmlkji--gfenm}, table:T00002: {0000011021.00/opqrstuvwxyzabc}/{0000011021/cMNOP} last successful match was 11020 mirror: 972715/972715 mismatch: table:T00001: {0000972715.00/opqrstuvwxyzabcdefghijklmnopqrstu}/{0000972715/mMN------v----edcbasi}, table:T00002: {0000972715.00/opqrstuvwxyzabc}/{0000972715/mMN} last successful match was 972697 t: FAILED: void table_verify_mirror(WT_CONNECTION *, TABLE *, TABLE *, const char *)/322: failures == 0