WORKAROUND THAT WORKS: for dual return files (self/spouse):
For all T3s: enter 100% ownership at top and then half of all values into boxes. (I also only entered capital gains in box 53, using the same value as line 21, half the total, instead of dividing the time periods).
Then values for line 68140 on T936 were correct and agreed with Schedule 3 line 17600, and I could NETFILE both returns.
