Cache usage exceeds configured value, operations stall, WiredTigerLAS.wt grows

Multiple tests are seeing a cluster of apparently related symptoms:

• During the last portion of a checkpoint cache usage grows to well above the configured maximum
• Operations stall, probably as a result of cache exceeding maximum
• The WiredTigerLAS.wt file grows without bound, and circumstantial evidence related to the use of the WT lookaside cache connects this with the previous two symptoms.
• FTDC data capture stalls

Three examples from two different apps: