Your question is in fact very generic: what kind of ancillary meta-information is copied and transferred with Copy & Paste? And, you’re right, this is exacerbated with list items.
I’d say that the complexity of the operation depends on your formatting skill. If you work extensively with styles, you’ll suffer less problems than with direct formatting and far less than with mixed formatting (styles + direct).
It also depends on the range of the selected sequence.
Rule 1: initial state
Formatting state at start of the sequence will define the inital state when pasting. Formatting state is made of paragraph style, character style and direct formatting at start of the selection. This state is part of copied information.
At the paste location, you also have some formatting state: character and direct formatting (paragraph style is ignored). Paste information takes precedence over the existing state. Paragraph style is unaffected because it is not part of state information. Character style replaces the one in effect, as does direct formatting if some existed in the copied sequence.
But, if your starting state at paste location (destination) had some direct formatting and none was defined at copy location (source), this direct formatting will hide eventual pasted character style and take precedence (DF always hides character style which hides paragraph style). This change in formatting always surprises newbies but it a natural consequence of precedence rules.
To avoid this problem, don’t direct format and always work with styles.
Rule 2: formatting changes are transferred
If your selected sequences contains style applications, such as character styles or direct formatting, the extent of style application is honoured. This means character styles or direct formatting stop their effect at their end boundary.
Rule 3: full paragraphs are unaffected
When your sequence contains paragraph marks, this is equivalent to a formatting change via some paragraph style. The pasted paragraph style replaces the one in effect at the destination location. Full paragraphs are then transferred unaltered. After the last paragraph mark in paste data, you’re back in rules 1 & 2 context.
Now how does this behave with list items?
If you copy only item text, i.e. you don’t include the paragraph mark, you’re under rules 1 & 2 which ignore paragraph formatting. Since numbering is part of the paragraph layer, numbering is not transferred to paste location because you have no paragraph.
Alternatively, if your selection include the final paragraph mark, rule 3 applies and you get a numbered list item, sometimes with an extra empty paragraph after it according to where you pasted.
Apparently, it does not matter whether numbering is done with direct formatting or style.
You seem to be familiar with Word. I want to draw your attention on the fact that Word has an insufficiently defined specification in a lot of formatting areas (in short, it knows only of paragraph styles and direct formatting, no character, page, frame or list styles). To ease conversion, Writer offers a one-size-fits-all compatibility feature for list formatting through Format>Bullets & Numbering or the equivalent toolbar buttons. This is unfortunate because the implementation has to face a lot of ambiguities. They are not apparent but lead you into “surprises” when you edit your lists with copy and paste. To avoid problems, prefer Writer list styles (badly names because they don’t format a list; they only define the properties of the number/bullet and need to be applied to some paragraph as associated to a style or direct format).
Proper use of list styles go beyond this question, so I’ll deliberately omit the discussion to keep the answer simple.
In case you have other questions, always mention OS name, LO version and save format.
