Copy/Paste error

From that linked page:

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Select a single note
In Normal mode, click on a notehead.
Note: Selecting a single note then copying and pasting it, will only copy and paste the pitch—not duration or other properties (such as stemless). To copy the entire note, including all properties, you need to hold down Shift—as for chord selection (below).

Select a chord
In Normal mode, press and hold Shift, then click on a notehead in the chord.
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If you click on the notehead you are selecting only the notehead. if you shift+click on the notehead you are selecting the notehead+stem+flags (if there are stems or flags) and you will see the whole of the selection in a blue rectangle. For the purposes of selection MuseScore refers to the selection in the blue box as a "chord" even if there is only a single note head.

If you select only the notehead and copy paste, you are only copying and pasting the pitch, the duration is determined by what you paste onto (a rest or a note). If you click on a quarter note C and paste onto a half note D or a half note rest you will get a half note C. If you paste onto a 1/8 note E you will get an 1/8 note C etc. If you shift+click you will select the note (or as MuseScore refers to it the chord) plus all its other attributes including its duration and any associated articulations. When you paste that all of the attributes are pasted with it. In this way if you shift + click and copy a quarter note C, you will paste a quarter note C wherever you place it.

If you have a quarter note C major triad and click (not shift click) on the E you can then copy and paste that E pitch onto a 1/2 note rest and get a 1/2 note E. If you shift+click on a quarter note C major triad you can then copy and paste the whole quarter note triad onto a 1/2 note rest and get a 1/4 note C major triad followed by a 1/4 note rest.