Hi Ben,
Two things to check--spatial index (does it look reasonable?) and try using sdelayer -o alter to update the layer's extent with the -E option.
sdelayer -o alter -l <table,column> [-e <entity_mask>] [-M <minimum_id>]
[-S <layer_description_str>] [-k <config_keyword>]
[-i {<service> | <port#> | <direct connection>}] [-s <server_name>]
[-D <database_name>] [Spatial_Index] [-L <ON | OFF>]
[-E <{empty | calc | xmin,ymin,xmax,ymax}>]
[-G {<projection_ID> | file=<proj_file_name}>]
[-P HIGH[{-R <SRID>|[Spatial_Ref_Opts]}]]
-u <DB_user_name> [-p <DB_user_password>] [-N] [-q]
Melita