For magical staves that can be targeted (e.g. volcano summoning, parting water), the staff disappears from the PC's sprite while the staff is being targeted.

EDIT: ASCII mode is also affected by the momentary unequipping. The staff's DV bonus will no longer be shown until the display in manually refreshed. For staff of the archmagi, its Mana bonus will not be shown until the display is manually refreshed. In both modes, zapping staff of the archmagi momentarily reduces maximum PP.