Was digging around and came across this thread - Slightly old but relevant.
You have in fact hit a CDC bug in SQL that affects all SQL Versions from SQL 2008 to the latest patch level on SQL 2014.
The bug will occur when you change a data type from TEXT to VARCHAR(MAX) on a table that is marked for CDC, and you then update any row to push the LoB value off page (ie total row size exceeds the page size). What makes this bug so damn sinister is that you could successfully do the table ALTER and then the problem will sit dormant till whenever you update that LoB column off page.
When the bug occurs it will manifest itself with a broken CDC Log Reader (ie SQL Agent CDC Capture Job) that will NOT move past a specific LSN.
There is no fix from Microsoft. The only way to fix it is to disable the table for CDC, and re-enable
As FYI - I have blogged about it here with a script to reproduce it.