fix(updating): don't validate computed values

[sisp]

I've fixed the update algorithm to always re-compute computed values in low-level copy calls, which fixes #1779 as side effect.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.65%. Comparing base (3216628) to head (8825f26).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1785      +/-   ##
==========================================
+ Coverage   97.63%   97.65%   +0.01%     
==========================================
  Files          49       49              
  Lines        5164     5196      +32     
==========================================
+ Hits         5042     5074      +32     
  Misses        122      122              

Flag	Coverage Δ
unittests	97.65% <100.00%> (+0.01%)	⬆️

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