Aerospikes being weird (?) 0.90

[TheXRuler]

I know I know I shuold get the new version (believe me I want to) but since Kethane seems to be discontinued, and please tell me if I am mistaken here, I am currently unable to upgrade since I still have ships with those parts on missions.

My "problem" is this. I just built an SSTO craft for laythe [insert smugface] using an aerospike. While testing on Kerbin I discovered something veeeery weird. As soon as I had finished my circularisation burn in LKO the sound and animation for the Aerospike changed (like I was running at 50%thrust) and it stopped using Oxidiser Oô I mean ... right? xD And while this might be a very usefull exploit if I am able to reproduce it I have absolutely no explanation for this behaviour. Has anyone experienced this? Is it a known .90 issue? I have certainly never heard of it ^^