I'm running OpenOffice 4.2.0.4 on Windows 7 (using the US-International Keyboard). 

When I run a Spelling and Grammar check in Writer, come across a misspelled word, and add it to a dictionary, other instances of that word in the Spelling and Grammar checker's text selection currently under review are still flagged as unknown. The dictionaries are apparently not checked again until the checker has moved on to a new text selection. 

Example:

The checker's text selection currently under review includes the sequence "Raggmopp! Raggmopp! Raggmopp!"

The first Raggmopp is flagged as unknown (not in the dictionary) and the user adds it to a dictionary.

The second Raggmopp is flagged as unknown, despite having been added to the dictionary.

Once the checker has moved on to a different selection (after the user has used the "Ignore Once" button), however, further instances of Raggmopp are no longer flagged.