The compatibility tests broke.
http://build.wiredtiger.com:8080/job/wiredtiger-compat-develop/824/
The reason is that the new chunk_count_limit is written into the metadata and the older versions error when encountering that in the metadata (as opposed to the basecfg). This is definitely an ongoing problem with new items not tolerated by older versions.
############################################ # RUN PARAMETERS ############################################ abort=0 auto_throttle=1 firstfit=0 bitcnt=5 bloom=1 bloom_bit_count=50 bloom_hash_count=17 bloom_oldest=0 cache=240 checkpoints=1 checksum=uncompressed chunk_size=8 compaction=0 compression=none data_extend=0 data_source=lsm delete_pct=17 dictionary=1 evict_max=0 file_type=row-store backups=0 huffman_key=0 huffman_value=0 insert_pct=65 internal_key_truncation=1 internal_page_max=16 isolation=snapshot key_gap=5 key_max=86 key_min=24 leak_memory=0 leaf_page_max=16 logging=0 logging_archive=0 logging_prealloc=0 logging=0 lsm_worker_threads=3 merge_max=9 mmap=1 ops=1000 prefix_compression=1 prefix_compression_min=3 repeat_data_pct=65 reverse=0 rows=10000 runs=1 split_pct=59 statistics=0 threads=2 timer=0 value_max=2549 value_min=11 wiredtiger_config= write_pct=25 ############################################