Cache capacitor allows you to cast ON YOUR SELF one spell for 24h (roughly)
and states certain spells to be cast that way (determined by your type of capicitor). also you need to spend a spell slot AFTER youve rested
life bubble has, since lvl 1, a duration of 24h/lvl and targets up to 1 creature/level and you can cast the spell BEFORE you rest
which makes the normal life bubble spell superior than the cache spell. also you get the Cache capacitor ability at lvl 6 which makes the whole thing even more senseless.
why though it is even possible? was that ability or the spell working differently in the sf beta?
Most likely it was different in an earlier iteration.
I'm not sure this is really a Rules Forum question, as much as a General question, though. There isn't anything unclear about how Life Bubble in a Cache Capacitor works, any more than there is reason to ever do it.
Not every single combination is going to be a good idea.