Each account has a default category, which you can specify when you set up the account. This will be the default whichever type of transaction you enter in the account.
I agree this does not seem ideal, perhaps Moneydance might wish to consider changing this in a future release?
But having said this, I have set up four categories for dividend income; regular and special dividend income for individual shares and similar for investment trust dividend income, so one default would not suffice for me.
To simplify things, I group all my investment categories under one main category and set this main category as the default for the account, which simplifies selection of the correct category as they are all immediately below the default selection.
Hope this helps a little.
Sorry, can't help with regard to the share price display.
I suspect you are seeing prices that are greyed out, if this is the case then they should just be placeholder values. Discussions have been had about these in the past and while I have no problem if placeholders are needed in the data I do not believe they should be visible.