In Qt 5.5.1 there is a bug with QSerialPortInfo::availablePorts().
how to produce this bug :
1 - open any serial port
2 - unplug the device
3 - read or write bytes
If you read or write bytes on an open unplugged port, you can't close this port, each operation return an error like DeviceNotFound or NotOpen, and this port is always present in QSerialPortInfo::availablePorts().
But if you close the port before Read/Write operation, everything is good.
This bug is reproductible with Qt serial port exemple.
This bug is not present in Qt 5.5.0.