When I run test/format with this CONFIG, I see a "next key mismatch" error. It takes a little while, but it happens, and after it happens, I can use the -r flag to test/format to repeat it every time.
t: process 29599
nextprev: next key mismatch: 0, insert 0, update 0, remove 0
bdb-key {0000000092.00/opqrstuvwxyzabcdefghijklmnopqrstuvwxyza}
wt-key {0000000050.13/opqrstuvw}
############################################
# RUN PARAMETERS
############################################
# bitcnt not applicable to this run
cache=20
compression=none
data_extend=0
data_source=lsm
delete_pct=26
dictionary=0
file_type=row-store
huffman_key=0
huffman_value=0
insert_pct=45
internal_key_truncation=0
internal_page_max=11
key_gap=3
key_max=64
key_min=13
leaf_page_max=12
ops=2000
prefix=1
repeat_data_pct=79
reverse=1
rows=100
runs=0
split_pct=72
threads=1
value_max=64
value_min=14
# wiredtiger_config not applicable to this run
write_pct=72
############################################