Intermittent - Error opening serial port - 1.8.8 portable

I intermittently get the "error opening serial port" error in IDE 1.8.8 portable on Windows 7 64 bit.
Arduino 1.8.5 does not have this problem. I can run them both at the same time or just either one, the issue follows 1.8.8 but I can't comment on whether it's related to my portable installation.

My only fix so far is to close (if open) the serial monitor and try opening it repeatedly until it opens. Then it works to flash the sketch and continue. I think I recall the error only appearing if the serial monitor was already open.

The report names no source files, tests, or entry points. Start by reproducing the serial-monitor and port-opening sequence on Windows 7 with IDE 1.8.8 portable, comparing it with 1.8.5 and checking whether the portable installation changes the result. Done means the intermittent opening error is reproduced and resolved without disrupting sketch uploads.

Written by the indexing model from the issue text.