when tcollect goes (sorta) buggy....

[parisse]

There is indeed a learning curve to control a CAS. The main reason is that there is most of the time no algorithm that will return in all cases what the user expect, for example for simplification, and the complexity of computations explodes very quickly.
I'm interested in experiences like those you report, they give me indications where I should put some safeguards if it is possible : I'll do that for simplify((sin(x-sin(x))')