MinimServer Conflicting Values in Filter Warning

[qblack]

I have recently created a tag ENCODINGTIME for all my music files to allow indexing of the month they were added to my collection. I initially populated it with yyyy-mm strings for my new rips. Then I got more adventurous and ran a batch process to dump every file's creation date in yyyy-mm-dd hh:mms format to the ENCODINGTIME tag (checking for errors where the day was not consistent for a whole album: some creation dates did not correctly reflect the original rip date).

I then added -EncodingTime:Month Added to the indexTags property. Finally, EncodingTime.yearMonth.index to the tagOptions property.

Now I'm seeing warnings in the log, such as:
Warning: sort value conflict for EncodingTime filter 2009-09
first conflicting value is '2009-09-16 10:36:30' in item 'Bruckner: Symphony #7 In E, WAB 107 - 1. Allegro Moderato'
second conflicting value is '2009-09-16 10:34:16' in item 'Bruckner: Symphony #7 In E, WAB 107 - 2. Adagio: Sehr Feierlich Und Sehr Langsam'

It seems that at least one of the conflicting pairs is in long yyyy-mm-dd hh:mms format so I'm wondering if the tagOption yearMonth is not coping with strings longer than yyyy-mm-dd? There are over 100 warnings in the log but I don't see any pairs (there are only ever two conficting values) where both are in yyyy-mm format.

Any clues?