In order for an objects grants to show up when exporting DDL, you go to Preferences>>Database>>Utilities>>Export and make sure than "Grants" has a checkmark next to it. One of our colleagues cannot get this to work. We've even gone in and deleted the ...\SQL Developer\.. folder and had him start from scratch.
I should mention here that it works for the rest of us. I can toggle the Grants checkmark on/off & see the effects immediately. I should also mention that my co-worker can see those same grants under the Grants tab when an object has been selected.
It looks like this setting is contained within ...\SQL Developer\system3.2.09.30\o.sqldeveloper.184.108.40.206.30\product_prefrences.xml, but those entries that have the string "grant" in them look the same as mine.
I can't think of anything else which will shake this loose. Unistalling isn't the easiest option, as we have the tool installed in Citrix.
Bug 14551896 - FORUM 3.2: GRANTS NOT SHOWING ON SQL TAB OF OBJECT EDITOR Bug 12583419 - CANNOT EXTRACT DDL GRANTS OF OTHER USERS IN SQLDEVELOPER (Enhancement Request) Bug 12596786 - NEED DIRECT SELECT ON TABLE-> GRANTS/DDL EXPORT OTHER USER? (Duplicate of Bug 12583419)
Unfortunately your SQL Developer release is 3.2.09.30 (an early adopter version!), but the issue was actually fixed for Bug 14551896 (which got included in 3.2.09.96), so if that is in fact your problem you will need to upgrade. As for it working for some users and not others in the early adopter version, according to the bug description, that occurs when some have SELECT directly granted on the table and others do not.
Please compare the actual system and object privileges for the users in question to see if this scenario applies.