I guess I misunderstood the post using weblinks in MB itself instead of sending that data elsewhere outside of MB
Edit: I've never used the Custom Web Links/Open in Web Browser feature seriously until now, so now I have a better understanding of what you're asking.
For example, I made a custom web link called OCremix to search the OCRemix site by artist name. Since OCremix.org uses a specific number for each artist, I have to use the search page instead of it directly linking to an artist page like some other sites handle.
That said, in my opinion, if the artists tag contains a URL instead of the actual artist name, then the tag itself should be corrected to the artists name. I've spent hours editing tags in my library because of incorrect/missing artist and such. Search and Replace is very helpful when needing to correct large amounts of mistagged tracks.
Most singles on OCRemix have http://ocremix.org
as the album title. I would never need to search the web for that via MusicBee, however, for shits ands giggles, I made a Custom WebLink for OCremix to just pull up the Album tag and when used on an OCremix Tag, it produced an error. I didn't read the error, but it may have produced those anomalies you had.
Edit 2: Did some further tinkering. Was able to make links for search Discogs by Artist OR Album with no problem. Had a Problem when I searched on VGMDB and noticed it converts spaces into "%20" in the url. This is necessary for most web search engines and works just fine for Discogs. I realized I had the Search URL incorrect for VGMDB
I was usinghttps://vgmdb.net/search?q=&type=
<Artist> &type= OR https://vgmdb.net/search?q=
This fixed it and made VGMDB search it properly.
I haven't tried it with a tag that has slashes or colons, but regardless, MusicBee NEEDS to do that in order to prompt the website to use the proper character in a search. And as I opined above, an Artist tag shouldn't be a URL (unless an artist's name is literally an URL).I think your problem is a tag problem, not a MusicBee Problem