Examiners bent on rejecting applications really do not like negative limitations. This is partly because negative limitations are extremely helpful in differentiating prior art in terms of both novelty and inventiveness. So these examiners often look for other ways to reject negative limitations. One common approach is for the examiner to assert that the applicant did not have "possession" of the negative limitation. 

Cabela's patent application 13/231,432 illustrates a recent example of these issues.  The invention relates to garments that incorporate a seat, as shown in the figure below from the application.

The claims included the limitation that the seat is connected to the garment by only the first elastic strap section, the second elastic strap section and at least one hinging strap. Of course, the figures showed only embodiments connected this way, but the specification did not use the magic word "only." The examiner considered this a negative limitation and thus asserted that the claim failed to have written description support. This is a common situation for applicants because the applicant realizes only during prosecution, after seeing how the examiner interprets the claims and applies the prior art, that it would be advantageous to limit the claims to requiring "only" certain features. 

Here, the PTAB agreed with the applicant that there was proper support for the claimed limitation. From the PTAB's decision,

Appellant's drawings consistently depict a seat that is attached to a garment by upper strap sections 56 and lower strap assemblies 48. See Figs. 1-7. Upper strap sections 56 correspond to the first and second elastic strap sections of claim 30. Spec. i-f 30. Lower strap assemblies 48 correspond to the hinging strap assemblies of claim 30. Spec. i-f 27. There are no other straps or connection means that connect the seat to the garment. Appellant had the requisite possession of the claimed subject matter as of the filing date of the application as the drawings show a seat that is attached to a garment by "only" upper and lower strap assemblies 56 and 48. We do not sustain the Examiner's Section 112, first paragraph, rejection of claims 30, 31, 48, 52, and 53. 

The only other wrinkle here was that the specification actually did describe another connection between the seat and garment, namely a buckle. However, the specification made clear that the buckle was "optional" and thus the Board determined that the optional feature did not undermine Cabela's position and the specification did support the claimed feature. 

So, when looking for amendments that might be characterized as a negative limitation, if the specification and figures have an embodiment that is consistent with the negative limitation, stick to your guns and do not let over-zealous rejection-prone examiners convince you to give up on your approach.