Why does autoroll affect my balance?

[UpQuark]

I have autoroll turned on for the first time (in Fidelity, for 4 week treasuries) and it looks like the process has temporarily made the balance of my core position unavailable (I still see the core position amount on the positions webpage, but the webpage for available for trade and withdrawal is showing as $0).

Is that normal? Will it happen every month?

 

[calmloki]

Also curious how Fidelity autoroll will work: If I have a T-bill that matures on Thursday and autoroll turned on and another T-bill due to settle it's purchase on the same Thursday I need nothing in my settlement account, right? I know at VG if I buy a T-bill at auction on Monday and have an equal denomination T-bill maturing on the settlement date VG says I can't spend the purchased T-bill's cost from my settlement fund. Then on Friday, after the sale and purchase both occur, the settlement account goes back to the old balance + "interest" on the sold T-bill.

 

[REWahoo]

I saw the thread title and immediately thought, "Why on earth would any aircraft have an 'autoroll' setting?"