Use of #pragma INTERRUPT with nc100 compiler

I'm develloping a multi-task application with µC/OS and try to use the #pragma directive to set up interrupt handler but I get an issue:

A way of coding that I tested and that works is to use assembly to enter in the interrupt:

void my_c_subroutine(void)
{
     ...
}
void asm_isr(void);
#pragma ASM
_asm_isr:
PUSHC       FB
PUSHM       SB,A3,A2,A1,A0,R7R5,R6R4,R3R1,R2R0                      // Save context
 
JSR         _my_c_subroutine  
POPM        R2R0,R3R1,R6R4,R7R5,A0,A1,A2,A3,SB                      // Restore all processor registers
POPC        FB
REIT
#pragma ENDASM

But if I do (to gain in performance):

#pragma INTERRUPT my_c_subroutine
void my_c_subroutine(void)
{
     ...
}

My program crash when returning from the scheduler

I have a look at the assembly code generated using the #pragma INTERRUPT directive and it look like that:

_my_c_subroutine:
PUSHM       SB,A3,A2,A1,A0,R7R5,R6R4,R3R1,R2R0
...
POPM        R2R0,R3R1,R6R4,R7R5,A0,A1,A2,A3,SB
REIT

I can see that the FB is not pushed, that explain why my scheduler can't restore the context of the task properly but I don't understand why the #pragma INTERRUPT directive don't save FB.