Why some primers in 'graphical view of primers' in the NCBI are represented as thicker lines?

Question

[Gerardo]

Hi everyone! I noticed that some primers in the graphical view of primers (pick-PRIMERS tool) in the NCBI are showed as thicker blue lines. What does it means? For example, in the picture, primers 7, 8 and 10 have a thicker blue line compared to others primers which are thinner.

[Mensur Dlakic]

All of them happen to be at the same level, yet I admire that you noticed it at all. I am guessing it is a rendering artifact.

[Gerardo]

In this particularly case it appears after I click in "You can re-search for specific primers by accepting some of the unintended targets, check the box(es) next to the ones you accept and try again to re-search for specific primers"

I'm wondering if this has to be with some primers being more specific than others