While frequently quoted on an annual basis for convenience, there are many depreciation methods that do not use annual calculations. When quoted on an annual basis, but used in a daily calculation, the rate is typically divided by 365 for the notional daily rate. This is what Manager does. (Some programs ignore leap years entirely.) See this example for 2016, a leap year. Depreciation of the second asset, for example, is (2950 x 0.20) * (366 / 365) = 591.62:
If the same worksheet is used to calculate depreciation for 2017, you get different results:
Manager calculates rates as designed. There is no bug on this issue. If you do not wish to use the method for which it was designed, you should make your own depreciation calculations and enter them in the Depreciation Entries tab.
That would only be correct if the program’s design adopted different conventions. In fact, the program does not base its calculations on a year, because depreciation is often calculated for different periods. Manager bases its calculations on the number of days in the defined period after deriving a notional daily rate for a 365-day year. Other accounting packages adopt a very wide variety of approaches to this problem, most of them either ignoring it entirely or requiring you to laboriously define your own calendar periods.
The current worksheet is not intended or designed for straight-line depreciation. That would require basing the depreciation calculation on acquisition cost (possibly less salvage value, depending on local law or accounting standards) rather than book value. So adopting your suggestion would not make it suitable for straight-line depreciation or any method besides daily declining balance.