Incorect time+timezone conversion?

I found a weird problem with Date field. When stored time is >= 00:00:00 instead of hour value, day value is incremented. I'll explain in detail...

My timezone is Canada/Central, currently it's -05:00 relative to GMT. When I enter a date into date field, eg. "Apr 18 2007 18:00" it seems to be stored in GMT as "Apr 18 2007 23:00" (+5 hours). Everything is fine here. When I edit, view my node it shows proper date/time: "Apr 18 2007 18:00". Same thing with all values from 00:00 to 18:00.

Now when I enter "Apr 18 2007 19:00" (i.e. "Apr 19 2007 00:00 GMT") it actually displays the node with date "Apr 19 2007 00:00", but still shows "Apr 18 2007 19:00" when I edit the node. Date would still show up correctly in edit mode, but not in view mode.

I'm guessing there's some sort of bug in conversion between timezones when GMT value is 00:00.

My configuration:

Drupal 5.1, Date 1.4, CCK 1.4, drupal's site time zone is left at default +-00:00, Date field's "Site timezone" is set to "Canada/Central", Date field's "Time zone handling" is set to "Site's timezone", type is "date", widget is "selector", not required, not multiple, "to date" is "optional" or "never".