When calculating my Capital Cost Allowance, turbotax gives me a lower base amount than the total (as if there were dispositions but there were none). Reason for this?

It should be:
UCC start of the year + cost of additions = base amount

Turbotax gives me a much lower base amount.
When checking my detailed return from last year I see that turbotax automatically included an adjustment (additions minus dispositions) but there were no dispositions!