Ink color contamination, cross contamination

http://www.mutoh.com/kb/entry/95/

This is a vacuum based system for the pumps. If the vacuum does not get broken a low ink cartridge may pull ink from a higher ink cartidge and lead to cross contamination.

Something similar can occur when the cap pad swells up and makes contact with the bottom of the head.

There are a couple of situations where color cross-contamination can occur.

Plugged ink drain lines OR
Swelling of pads in the capping station.
In combination with uneven ink levels in the cartridges.

The most common one that I am aware of is swelling of the pads in the cap itself.

There are two layers of pad in the Falcon series printers.
The top layer can be carefully removed to buy time before the cap itself need replacement.

The pads are not available as a separate part #, but the caps are.
Usually, by the time you are having issues from lack of proper maintanence or just use, it makes more sense to replace the entire station.