Hi Paola,
sorry, the new year started turbulent... 
This is really strange. Is think in the same direction as you. However if you search "linda 2", I assume, that you find other two materials as well, because it may be equivalent to "linda AND 2", i.e it's find linda and 2 separately in the material description (or character 2 even somewhere else)
If you using asterisk, it tries to find the whole string in the same attribute and finds only one material where linda and 2 occure together.
But what I don't understand is, why if you search "*linda* 1" it finds all three materials. According to my logic it should find only two, since the first has not the character 1 in the material description?
Can you recheck this query? If it still deliver all materials I would suggest you to open the OSS message, because my logic skills are at the end
Thanks and best regards,
Artem