We have essentially three aspects here:
What is the optimal formatting of that title?
First, one (reasonable) formatting paradigm for all titles and posts is advantageous for readability and is something to strive for (though to what extent is debatable, see below).
Now, the paradigm according to which these verbs would be capitalised would be one that does not only include title casing but also capitalising German words¹ in English sentences according to English rules. As per this Meta post, sentence casing for question titles is community consensus (with good reasons, in my opinion). Moreover, applying English captialisation rules to German words hinders reading and may cause confusion. So neither requirement for capitalising all verbs is fulfilled.
Finally, when referring to a word itself, we usually mark this in some way (preferrably italicising), however for titles, we can only use quotation marks. Thus we arrive at:
“Senden”, “schicken”, and “verschicken”
Arguably, this is not the nicest formatting since we have many quotation marks and it is quite apparent that you are referring to the words themselves. However, in my opinion this is the lesser evil in comparison to having an inconsistent formatting.
Do you have a right to format your title the way you like anyway?
Yes and no.
You may write your questions with whatever casing you like but you cannot require them to remain like this. As soon as you post something, it becomes the community’s. To quote from the FAQ:
If you are not comfortable with the idea of your contributions being collaboratively edited by other trusted users, this may not be the site for you.
Also note that addressing issues such as title casing in a meta post and voting on the answers is how we as a community make rules here (unless they are overruled by a comparable decision on a per-site meta or StackExchange itself). If you dislike this, you can still offer the alternative as an answer (with good arguments).
In another argument, consider the case that somebody insists on a question title to be in all-caps. They are particularly difficult to read, half the Internet feels shouted at by them and they stand out visually on any list. Is there a written-in-stone rule that you have to sign before creating an account that all-caps mustn’t be used? No. Should we decapitalise all-caps question titles, no matter what the OP prefers? In my humble opinion: Yes.
Should questions be edited to fix title casing?
Edits bump questions to the front page and, if they come from users without editing privileges, they also require approval. This creates noise and work and should be taken into account when changing aspects with little relevance (which probably everybody here agrees is the case for the casing of your question title). Thus, I think nobody should have edited your question for the sole purpose of changing the casing.
However, this also applies to you: You should not edit your question for the sole purpose of changing the casing – in particular against the community norms on formatting. Moreover, if you know that an edit is against the community consensus on formatting, you should not perform it.
On the other hand, if somebody edits the question for a good reason anyway (e.g., to fix a spelling mistake, which is crucial on this site), they are absolutely free to change the casing towards the community norm. Thus, the edit performed by Ingmar was perfectly acceptable.
¹ When referring to the words themselves. Loanwords are a different thing.