allwinner h616 + serial console glitch

i have started to play / hack support with a h616 (an android tv box in fact)
i managed to get usb, sd, e-mmc, clocks, gpio to work
no ethernet and axp/power controller yet

but the problem i have besides not having a proper dtb (the android image extracted one is not exactly usable because of different notation, device names, etc) is a serial console glitch
in the form of not echoing the last character typed
you always need to type +1 character to get the desired input
so to login you type root\n<firstcharacter of the password> and then you get the password prompt
so you type n+1 characters to get n characters sent

the bug is not present in u-boot/loader just after the kernel started
the uart to ttl dongle i use in the pc is good, i tested it with other boards and works as expected
the board does not have a pin header for the connection just holes and i stucked the wires in the holes without soldering (very flimsy but still works in u-boot) also rx works ok

does anybody know how to fix the serial connection ?