Strange effects DDE C long long

I am facing strange effects (in my opinion) with a sequence written in C compiled by Norcroft C:

unsigned long long temp_time;

…
temp_time=(unsigned long long) regs.r² & 0×00000000000000FF;
→ r2 59 temp_time 59 (hex)
temp_time=temp_time<<32;
→ temp_time 5900000000 (hex)
temp_time|=(unsigned long long) regs.r³;
→ r2 59 r3 b519ae10 temp_time ffffffffb519ae10 (hex)

???

I would have expected 59b519ae10 for temp_time. Sometimes temp_time is correct. I assume that this
is the case if Bit 31 of r3 is 0. However I expected that because of the type declaration this won’t play a role.

What I am doing logically wrong?

I’ve been caught by that one before! Stepwise promotion is your friend:

temp_time |= (unsigned long long) (unsigned int) regs.r[ 3 ];

Thanks for the hint! Of course as an alternative I can AND 0×00000000FFFFFFFF. But I wasn’t aware of that behaviour :-(. Easy to forget …