The client is super strange. Despite rewriting the Mag format for GC, Sega still didn't pick a sane format. For whatever reason, when you're feeding a Mag in your inventory, the bars are represented by 100 points, and items are allowed to give an odd number of points. When you put the Mag in the bank, quit, or go to the lobby, odd values are divided by two and remainders are discarded, because the Mag data stores the bars out of 50 points, rather than 100. When you start the game again, make a new team, or take the Mag out of your bank, PSO doubles the Mag's bar stats to put them back on a scale of 100 for subsequent feeding.
Somehow the client is able to track your feeding bars out of 100 when your data is in limbo (not saved), even though the actual Mag data doesn't support that. You can use this quirk to raise Mags in an insanely slow fashion to get a few extra points of POW or MIND than you could otherwise: if you feed your Mag only one mate or fluid (which likely gives an odd amount of DEF, e.g. 5) and then bank it, the rounding mechanism causes the DEF to decrease by 1, so when you withdraw your Mag, it only gained 4 DEF, rather than 5. Banking your Mag resets the feeding timer, so you can only feed one item every three minutes this way, but it does allow you to get about 3 extra POW or MIND than if you just fed your Mag three items at a time.
As far as I can tell this behaviour is totally insane, but you have to copy it in the server, or you'll never be able to escape Mag feeding desyncs where you withdraw your Mag and find that it either has different stats than it did before or that it didn't evolve the way you thought it did.