Dear community,
I encounter a strange or maybe logical behavior when calling a transaction thought a target mapping and passing parameters.
The transaction in question is FMCB and the field I'm aiming to initialize is P_SIMUL

Domain of this field:

My target mapping: ZFMCB-manage with the parameter Test that maps to P_SIMUL

So the issue is linked to the selection screen initializing the field:

So when I pass a parameter:
#ZFMCB-manage?Test=<empty nothing is here after the =>
It takes it as 'X' as the default value:

I tried several other values: single quotes, double quotes, null, NULL, SPACE, <just a space>, %20 (ASCI code for SPACE) the all end up like this:

The first letter/character of the value of the parameter is passed as a value of P_SIMUL.
If somebody knows how to solve this issue or knows how to pass a parameter to initialize the value of P_SIMUL that would be great.
Kind regards
Jérémy