This is what I did:

1. Created a party of four fighters and fighter multiclassers as well as two clerics
2. Gave all of the party's gold to the clerics.
3. Went to Training Hall and removed the four fighter-type characters from party
4. Went to the weapons and general goods shops to equip the clerics
5. Went back to Training Hall, re-added the four fighter types, traded the clerics' remaining platinum to them, and removed the clerics from party.
6. Went to the weapons shop and tried to have one fighter buy some banded mail from non-pooled funds.

This was the overflow bug that arose from pressing "b" for Buy:

1. Platinum, gold, silver, and copper changed into the millions or some other odd number.
2. Encumbrance was also in the millions. Movement was in the thousands.
3. Equipment list showed millions of some random pole-arm, already Joined although such weapons don't Join into stacks in the equipment list.
4. On the character page, where it indicates status (usually "Okay") there was a full edge-to-edge horizontal line of garbled non-alphabetic characters including many solid green boxes where a character could not be displayed.

I was partly able to reproduce this problem: from a saved game of the same party I couldn't as the previously removed characters had been added, but did create a new party that reproduced the problem as above.

Anyone know what even happened there?