Halve and double duration shortcuts (with or without dotted values)

There seems to be an inconsistency between behaviour of these shortcuts when in note entry mode.
1. I enter a stream of crotchets.
2. To follow this with a quaver (or stream of quavers) I enter Q. The next note I enter is indeed a quaver - which is what I expect.

But:
1. I enter a stream of crotchets.
2. To follow this with a dotted quaver, I enter Shift+Q. In this case, the last crotchet I entered is shortened, which is not what I expect - I have to go back to correct it before entering the dotted quaver I wanted.

The same behaviour occurs with other durations and with W and Shift+W.

Is this how things are supposed to be, or is it a bug? I have detected this on 4.4.4 and on 3.7

Thanks