test/format failure: illegal cell and page type combination

Just saw an interesting test/format failure that I'd like to chase further:

```
270: table, variable-length column-store                                     
t, file:wt.wt, session.checkpoint: illegal cell and page type combination: cell 8 on page at [write-check] is a value/ovfl,rm cell on a row-store leaf page
t, session.checkpoint: table:wt: WT_ERROR: non-specific WiredTiger error
t: session.compact: WT_ERROR: non-specific WiredTiger error
############################################
#  RUN PARAMETERS
############################################
# bitcnt not applicable to this run
cache=40
compression=snappy
data_extend=0
data_source=table
delete_pct=7
dictionary=1
file_type=row-store
hot_backups=0
huffman_key=0
huffman_value=0
insert_pct=34
internal_key_truncation=0
internal_page_max=13
key_gap=16
key_max=64
key_min=12
leaf_page_max=12
ops=5000
prefix=1
repeat_data_pct=49
reverse=0
rows=100
runs=0
split_pct=52
threads=20
value_max=256
value_min=19
# wiredtiger_config not applicable to this run
write_pct=45
```