Serial Monitor fails to set 250000 baud rate with error message.

Bug Report

Arduino 1.8.16
Linux Mint 19.2 (Ubuntu)

Arduino IDE serial monitor throws error "_Error while setting serial port parameters: 250,000 N 8 1" when setting baud rate to 250000_". It doesn't do this when selecting any other baud rate up to 2000000. With any rate other than 250000 the monitor comms work OK.

If another App is run first using the 250000 baud rate on the same port then closed and the Arduino IDE is started, the serial comms all works as expected at 250000 (error message still displays though).

No source file or test is named. Start by reproducing the failure in the Arduino IDE serial monitor on Linux Mint with a 250000 baud rate, then trace the serial-port parameter handling. Done means the monitor accepts 250000 without displaying the error while existing baud rates continue to work.

Written by the indexing model from the issue text.