Okay, so this one is super-obscure! TCC crashes, extremely infrequently, on a SETLOCAL. It happens only very rarely, but I can reproduce it. This only seems to happen when the entire environment -- including the current directories for all drives and the current value of CMDLINE -- is some specific size. So whether or not the crash occurs depends on exactly how the last command was invoked (e.g. TEST.BTM versus plain TEST), the current directory on all drives, whether or not TCC is running in a Take Command tab window (the TCMD and TCMDVER variables), and God knows what all else. I'm not certain exactly what the lethal size is, but it's somewhere close to 2048 bytes. If I do a SET > ENVIRONMENT.OUT immediately before the offending SETLOCAL, I get a file 2,062 bytes long (//UnicodeOutput=No). I honestly don't know whether this is something new in 13.04.55, or whether it's lain dormant for decades and I've only now stumbled across it.