Two identical Arduino UNO modules with different serial port behaviour.

Hi Experts here,
I am a bit baffled. I have got two identical Arduino UNO modules and they behave differently.

The first one, shows up as an Arduino UNO at COM3 and accepts uploads at 56KBaud.
Then I remove that one and plugs the other one at the same place.
That one shows up at COM4 and the same sketch wants to upload at 115K and fails.

In Windows I have exactly the same settings for both COM ports: 9600Baud, 8 data bits, no parity 1 stop bit.

I believe both modules used to work, somewhat must have changed the settings on the second module.
It does not really appeared to be broken, anyhow it communicates with Windows and shows up as an Arduino-Uno, so the basic communication must be functional, isn't it?.

The module that refuses to communicate has a lighting led13 and I tried to reinstall the boot loader, which failed.

How can I recover that?
Have someone's got a clue?

Thank you in advance

Try bootloading them as Unos again. Use Nick Gammon;s bootloader installer sketch.
http://www.gammon.com.au/bootloader