I have tried to reproduce your problem (as I understood it to be)in SP4.
New product with 3 parts:
1 Single (no links)
1 Parent (no links)
1 Child (contextual link to P)
Constraints behaviour :
S-P
normal updates, P drives C as expected
S-C
normal updates, apart for the constraint that...
We just updated from R17 to R18 SP4.
1 Text editor - yes, Enter works as OK button - for extra line <Ctrl> + Enter
2. Hot key for Redo - yes it does not work - I used Alt+z for Repeat for years ,and this seems to work
3. Measure tool - Tools/option/Param.and Measure/Measure tools - verify...