Inconsistent possibility to add a word to the custom dictionary

[Sheaper 1]

Hey, I honestly don't know if this is just a terrible implementation or a bug.

The note and spellchecking is obviously in German, but I don't think that this has any impact on the result.
The first screenshot shows a right-click on a wrong word ( either the "e" at the end is to much or its missing an "n"). The choices are good and its fine that I can add it to a custom dictionary ( "Zum Wörterbuch hinzufügen" in German).

The second screenshot is a Problem:

It shows a right-click on a word that is correct, but so uncommon ( its a compound word) that it has no dictionary entry. This is fine. BUT why in the ***** world cant I add this ( or any other word I like) to the dictionary ???

[tmtowtdi 0]

Same problem here. 

I'd like to have the spellchecker on for most note types (upcoming tasks, personal journal, recipes, etc).  But I also take notes on programming tasks and computer games, both of which feature non-standard vocabulary that is sometimes not recognized by the spellchecker at all, so I can't add those words to the dictionary.

Being able to disable the spellchecker for just a note or, even better, a notebook, would probably be good enough.  I do want the spellchecker turned on for those normal English notes, but being able to just turn it off for all notes under a given Notebook (eg "Gaming") would be fine.

My Skyrim notes are riddled with the word "dovahkiin" in a red underline.