The oval is clearly flat at the bottom (underlined in red). From the colors and frame it must be printing 5. Perferations look like KII row 5. Checking the complete sheet of printing 5 available on this website quickly revealed that my stamp is position 35.
I was surprised that this flaw has, to my knowledge, not been described before. I decided to try to find it in other early printings by going through the various complete sheets available on this website.
I think the same oval flaw is present in printing 1 in position 20: I believe it is also present in printing 3 in position 46: I could not find it in the partial sheet from printing 4 and also could not find it in the whole sheet of printing 6.
This raises the question: is this an oval flaw on a previously undescribed kliché or is it part of one of the already described klichés? I went through Tofdata 8.08 looking for klichés with known characteristics which are not present in Printings 1-6. There were several. Looking at real stamps and images, it looks like the same flat region is seen on stamps with OF.1.10.
There are no whole sheets available for printings 7 or 8.
In printing 9, the stamp with OF.1.10 also has an oval which is flat at the bottom: The same is true in printing 10 although not so obvious: and 11 where it is quite evident: By printing 12, the flat region cannot be seen: I was terribly saddened to learn of the death of Lasse Nielsen. His contributions to our hobby are immense. I especially find Tofdata to be extremely useful for working with the bicolored stamps. I hope someone is willing and able to continue updating the database and sharing it through this site. If so, this post can be my modest contribution to the next release (version 8.09?)
Comments in Danish or English are most welcome.