Unexpected use of &= causes error or crashes server

We had a typo in some old code to concatenate a couple things that basically looked like this:

The mistake here is the second &= that should just be a &.

Under ACF 10, this works.

Under Lucee 5 running on Tomcat 8.5.3 on Windows, it crashes the whole server with a core dump that begins:

Under Linux, Tomcat is fine and Lucee reports a java.lang.verifyError error:

http://i.imgur.com/SsjncPc.png

Arguably, nobody has any business doing a &= b &= c to begin with, so this certainly isn't a priority, but given that it brought down Tomcat on our Windows box I figured I'd report my embarrassing typo that ACF let me get away with for so long.