DeltaTime returns inaccurate time when Tick Interval is positive

When disabling/enabling tick at runtime, if (TickInterval == 0) then DeltaTime returns as the length of a frame, but if (TickInterval > 0) DeltaTime returns as the length between when tick was disabled and when it was re-enabled

Regression:
No - same behavior occurs on 4.15.3 (CL 3450819)

1. Download and unzip attached project
2. PIE
3. Hold "T" for a couple seconds then release to run script from "TickInterval_0"
4. Hold "Y" for a couple seconds then release to run script from "TickInterval_1"

Result:
DeltaTime returned when Y is released is the time since last time the actor ticked

Expected:
DeltaTime returns time since last frame