there are some irregular behviors around blocks; here is one where inserting a horizontal line in front of 2 horizontally aligned blocks deletes them 😵

you see it in the screen recording.

(btw., another issue in such a situation: while I can select 2 horizontally aligned blocks via cmd-shit-click, there is simply I see to select them via keyboard – unlike with vertically lined-up blocks… try it yourself…)