killed the beast!
Male - 22 Years Old
As someone who has followed this very closely, and actually wrote the Go Radio Wikipedia page and a lot of Mayday Parades, I feel like I know most of the situation. Most of the drama is from after he left the band.
In addition to his father, Jason was also about to get married to his now ex-wife Katie. In general he was burnt out on music and being in a band. I think a lot of it had to do with him thinking it was time for him to settle down. And while he wasn't given any credit for writing, and is listed as "Additional Vocals and Guitar by Jason Lancaster" in the ALIR credits, the album was released after he left the band. So I'm not sure how much of that had to do with it.
Personally I think a lot of it did have to do with recognition, he was the driving force behind the band yet Derek was getting all of the spotlight. That would bother anyone (I know it would piss me off personally). They split vocals down the middle (Jason maybe even sang more) on their first EP, Tales Told By Dead Friends. Yet on A Lesson in Romantics, he was clearly the second singer. I remember during a Mayday Parade band chat here a while ago, one of them said that they disagreed a bit while recording ALIR with the direction the album was going or something like that. I wouldn't be surprised if Fearless had anything to do with it, wanting Derek to sing more since his voice is a staple of the genre.
Anyways, thats just how I see it.