HP Prime lockup (not a complaint)

[Anders]

hi

I have similar experience in CAS with an other computation:

I am trying to calculate and simplify a trivial differentiation in the complex space
∂(√(z-i))/∂z , where z ∈ C
The answer should be: 1/(2√(z-i))
Trying different ways in the PRIME:

In CAS mode entering:
diff(√(z-i),z)
results in some wacko answer:
1/2*(()*diff(im(z),z)/(re(z)+√((re(z))^2+(im(z)-1)^2))+()*(-(diff(re(z),z))-1/2*(2*diff(re(z),z)*re(z)+2*diff(im(z),z)*(im(z)-1))/√((re(z))^2+(im(z)-1)^2))*(im(z)-1)/(re(z)+√((re(z))^2+(im(z)-1)^2))^2)*√(2*(re(z)+√((re(z))^2+(im(z)-1)^2)))+1/2*(diff(re(z),z)+1/2*(2*diff(re(z),z)*re(z)+2*diff(im(z),z)*(im(z)-1))/√((re(z))^2+(im(z)-1)^2))*(()*(im(z)-1)/(re(z)+√((re(z))^2+(im(z)-1)^2))+1)/√(2*(re(z)+√((re(z))^2+(im(z)-1)^2)))

simplify(diff(√(z-i),z)) results in a dump followed by lock up which I have to reboot to recover from.
What am I doing wrong here?

Interestingly the prime have not problem calculating:
diff(√(z-1),z) where z ∈ R (I assume Prime assumes R) which results in the correct:
(1/2)/√(z-1)

My Prime has the following configuration:
Model: NW280AA
Software: 6975
Hardware: A
CAS: 1.1.2-11
OS: SDKV0.44_R.521
CAS settings are:
Complex: ticked
Use i: ticked