numeric custom priority field causes error on sort

I created a custom priority field that stored numbers in the form x.yz (so 1.01, 1.23, 4.99). If I click on the column header in the dashboard, an error is given:
An error occurred searching: java.lang.NumberFormatException: For input string: "1.51"

I prefer the default sort order to be on priority, so this is hindering usability of the product to a great degree, especially as the list gets large.