Artificially running out of passive ports under load

When loading the FTP server with 200 users that are downloading files via FTPS in passive mode (implicit), the server eventually appears to run out of passive ports. FTPD log shows numerous instances of "cannot find an available passive port" (see txt attachment). While embedded, it appears the ftpd server also has a memory leak (separate heap dump available upon request - file is too large to attach)

Can be reproduced using JMeter with the attached testplan/ftps plugin in roughly 35 minutes.