TYPO3 Core

In that case at least an error message should be shown.

Patch set 2 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/29946

Markus Klein wrote:

How would you select two elements if you only display 1 (size = 1).

That configuration does not make sense.

true

size=1 means that I want a list of size 1. More could be made visible by scrolling. This is what I want.

Unfortunately, the implementation of the list-with-size-1 in TYPO3 through browsers creates a dropdown, which is unfortunate as it removes the possibility to select multiple entries.

Still, my wish to be able to select multiple entries should be cherished. A solution would be to increase the size of the HTML select element to 2 instead of 1.

Did you try to build an HTML select with multiple and size=1.

Give it a shot and modify any dropdown in the forge update screen.
Example:

<select name="issue[status_id]" id="issue_status_id" multiple="multiple" size="1">
...
<option value="1" selected="selected">New</option>
...
</select>

Looks really lovely: Some strange element on the screen, no scrollbar. You can navigate with the arrow keys or the mouse wheel, and you've no clue what actually is selected and what is available. Worst UX ever.