I have seen that back in the R14/R15 days but it was not limited to ribs. Is there fillets in the bottom of the ribs? Have a look and see what the properties tab of the view is set to in regards to fillets.
Win XP64
21SP7/22SP5, 3DVIA Composer 2013X, ST R20
Dell T7400 16GB Ram
Quadro FX 4800 - 1.5GB
Have you checked the drafting options that control whether a feature below a certain size is generated?
There is a setting that reads "Only generate parts larger than".
Any element smaller than the limit set in this option will not be created on the drawing.
This is great for large layout assembly drawings - but it can be confusing for detail drawings.