Tag synonyms and searching

In relation to an ongoing election, this post was mentioned: Include information about elections in the newsletter. One of the tags on that question is newsletter, which is a synonym of community-digests.

I have noticed that:

• Searching for [election] "cast your vote" shows this question among the results.
• But if I replace the election with newsletter or community-digests, that question is no longer among the results.
• Trying newsletter "cast your vote" returns some results, including the question mentioned above - here I am searching for the word newsletter, not within the posts tagged newsletter.

Is this caused by the tag synonym?

Personally I would consider this a bug. (I'd expect that the two synonymized tags should behave more or less equivalently. At least, I would expect that one of the two searches should return this question.)

I am aware that I can find posts with the tag newsletter using SEDE and in the same way I could search for a specific string in the given tag. However, it would be more natural to have a possibility to find such post using the search function on the site.

Of course, if the cause is something different or if this is the expected behavior, I have no problem with retagging this question from bug to support.

After a recent conversation in chat it seems that I should probably clarify the question a bit. I might be wrong, but it seems to me, that problem like this happens in the following situations:

1. The post was tagged with a tag.
2. The synonym was created later (and the synonymized tag wasn't merged into the master tag).
3. And the post wasn't edited since then - so it still has the "old" tag.

Here are some other examples from this site I was able to find. (The links are always first to searches with the two synonymized tags and then for some other tag.)

• encyclopedia with canonical-questions, canonical and self-answer (see this post).
• gamedev with exploit, security and sock-puppets (see this post)
• timestamp missing with date-format, dates and ios-app (see this post)

Some other related posts:

• What are differences between synonyms with and without merging from the practical point of view?
• How to find a question by its old tag when that tag is synonymized with another (Meta Stack Overflow)
• Converted tag synonym don't allow to filtering on converted tagged threads (Meta Stack Overflow)