Actually the list of the five threads is not the list of results of the searching while using the keyword specified in the top line. These are suggestions only and may not have too much in common with the keyword typed. The Search option tries to prompt you where your searching may start from. Also the option takes the number of letters in the keyword into consideration while trying to match words. The minimum is four or five letters as memo serves. Try to type the "lighting" for instance. As the result you should get the five suggested threads with the word "light" in their titles. No matter if it is the "light", "lightning" or "lights".
The word "p-38" contains 3 of them only while the "-" is treated as a special sign and is not taken into account for getting the suggestions. Because the "p" is the first letter it used for the searching. So the final result for the suggested threads looks like you posted above and me below. Please note that all the threads contain the "p" letter in the sentences. Also your thread has been added to the suggestions as it is the recent one and contains the "p" in the title. The full keyword ( with all its signs) is taken into accound for searching when you hit the "SEARCH" button at the bottom of the search window.
I hope my explanation is fine and you could grasp that.
View attachment 655797