This issue has been observed in CA PPM 18.104.22.168 and reproduced in 22.214.171.124.
This issue has been reported to Engineering as DE38843.
This defect has been fixed in CA PPM 15.4.1.
Edit the matrix, change any one attribute and save. Change back to the original value and save.
This will remove all the unwanted spaces saved in database and after that there will not be any problem in finding a matrix match as desired.