### Solving system of ODE gets "ValueError"

I'm trying to solve a system of ODE using desolve_system but get "ValueError":

t=var('t'); f=function('f')(t); g=function('g')(t);
de1 = diff(f,t) == f*sin(t);
de2 = diff(g,t) == 0;
desolve_system([de1, de2], [f,g])

gets:

Traceback (click to the left of this block for traceback)
...
ValueError: The name "+" is not a valid Python identifier

the problem seems to be sin(t) factor, without it the system solves with no problem. Also desolve(de1, f) has no problem. What is going on here?

Thanks in advance!