Crazy time display issue

Written a plugin that outputs a time field, strange thing is though that it does something strange for 7:00 to 8:59 times.

<li>{event_start_time} to {event_end_time}</li>
<li>{event_start_time}</li>
<li>{event_end_time}</li>

The above template code outputs as follows:

7:00 pm to "" pm
7:00 pm
8:00 pm

As you can see the first line kills the {event_end_time}, but only when that time ouputs anything between 7:00 and 8:59. Also to experiment I typed in “7:00 pm” instead of using the tag and the same result! So something in the template output processor is killing 7:00 to 8:59.

Anyone have ANY ideas why this is happening?