if you scroll down, kanji for しゅゆ is 須臾 which is the other form (or kanji) for しばらく. so I dont think it's bug.
I don't think that's how it's supposed to work. If you search for hiragana, it's supposed to bring back words that contain those kana. For example, if I search for せつ it doesn't bring back 雪 even though that's technically a reading of that kanji.
Setting aside whether or not that's how it's supposed to work, I'm not sure that's a completely equivalent comparison, since せつ is not a reading for 雪 as a standalone word.
Thanks for reporting this. It's because at one point the しばらく entry also had しゅゆ as a reading. It was split out into a separate entry, but Jisho doesn't clean up old search indexes. It's one of the main things I'm fixing with the next version of the site.
For now I've manually fixed the data so しばらく no longer comes up when searching for しゅゆ.
しばらく comes up in a search for しゅゆ
As the title implies, if you search for しゅゆ, the first result you get is しばらく even though it does not appear to contain "しゅゆ" in either the main nor alternate spellings. The meaning is similar so it's not strictly wrong, but it still feels like a bug.