There are sequences programmed to happen inside a period of time. If the sequence is broken, those blue screen wishes take place.
The same always happen to me when I for example train a toddler all in the same first life-day. Of course I cheat heavens and the 4 days become too long for the toddlers, so they wish "blue". The romantic is always the same, if they wish a kiss, they will then wish make-out and the last is woohoo.
A problem I'm starting to deal with the chemistry problem. If my Sim has first kiss or woohoo with another not-matching Sim, they will continue wishing romantic with this Sim even after getting married to a matching-one. The worst I had with the maid Kaylynn. In my game she is always from Family Aspiration but she always wish romance with previous relations.
On the end, I found out that Family Sims are much more available for prostitution than Romance Sims. To deal with wants and fears are quite troublesome. There's something similar to "cases count", I mean the game seems to count some interactions and I didn't really understand how.
On one of my test I created a Romance Sim and never allowed him to make woohoo, instead I used always "Try for Baby". It is not the same interaction and Try for Baby doesn't count internally as woohoo. My Romance Sim stopped wishing woohoo and as results were mostly obvious (many babies), he became a loveful parent always having wants and fears related to his children.
It is quite a comprehensive test aiming the possibility to develop sort of Sim's individuality. Maybe I'm wanting too much from the game, but I also have my own Wants and Fears.