ORA-01830 after changing date format to yyyy-mmm-dd

I changed the date format at the user level on the user preferences page.

The default was dd-mmm-yyyy and it is now yyyy-mmm-dd.

Since then, I get the following error when my one of my custom OAF pages tries to load (many other custom pages work fine as do Oracle-supplied pages):

ORA-01830: date format picture ends before converting entire input string

Through debug I have confirmed that the error occurs when the vo.initquery is executed.

I tried the following already and got the same result:

making the data type on the VO columns = 'Date'

making the data type on the VO columns = 'String'