There I was, going through Português Em Foco, Unidade 12, about the PPS, and it suddenly dawns on me that verbs that end in -çar , -gar and -car get weird for what I see as a good reason.
Notably that C and G can have hard and soft sounds depending on the next vowel. And to keep the same hard-softness of the c or g in the conjugations, one has to replace some letters.
Example - ficar - hard c - 1st person singular PPS - ficei would have a soft C - so it gets replaced by qu to keep the hard c sound - fiquei.
Once I saw this, I suddenly saw many other verbs with this pattern. C becoming qu, ç becoming c and g becoming gu…
Damn!!! A pattern!!!