That’s an inventive way to categorize words. I’m afraid I wouldn’t describe it as a bug though since it sounds like the system is behaving as designed. Each session is a maximum of 25 words/phrases, and if you start a new flashcard session from the Practice tab there’s no way to filter by words containing certain characters. Right now the only way you can prioritize learning of certain words is by starring (favoriting) them which will make the spaced repetition scheduling algorithm prfioritize them above the rest.
I’ll take the feedback on board though and will consider more fine grained categorization (beyond just starring words) in future. (No promises)