Updating my Mavericks machine to latest NoZAP-Pl2303-10.9-installer.dmg [size 7.2Mb] my app started failing on comms. I found bytes lost on input quite frequently, always pairs of bytes.
Reverting to osx-pl2303-0.3.1-10.4-universal.dmg [size 127Kb] my app works perfectly.
It seems this driver is suffering from 'Microsoft bloat' even though it is on Mac OS X 10.9.2
Incidentally both versions appear to be afflicted by a problem: If the receive buffer (I assume it is in the driver) fills and IOCTL FIONREAD returns 1020 then no amount of reading will empty the input. As I am using Java I cannot easily call tcflush so only unplugging the adaptor seems to work.
Can you please send me a test-suite so I can reproduce your problem. It can be caused by a "fix". In my test-suite the driver works perfectly.
I've been testing the NoZAP 1.4.1 beta driver for Yosemite, and also seems to experience similar problems with this driver. When copy/pasting commands to 9600 8N1 connected gear it seems to skip characters quite often, forcing me to paste in one line at the time, and even that amount of data seems to corrupt the input quite often.
I've been using an older version of this driver earlier with the same USB-serial adapter with no big issues.
Thanks for the hint how to reproduce the problem so I can fix it.