Huh? If you want to play a loop at different bpm's, the time selection should of course keep the position. Anything else wouldn't make sense since the loop start and end have to be the same, only the playrate changes. That means the audio or midi items get stretched or squeezed depending on tempo.
Maybe you mean the items stay the same while the time selection just sticks at its place and gets shrink or stretched? Make sure you work in the right time base then! You can change the time base at three places: project settings, track context and item context. From last to first the priority gets lower. If you want to hear the loop at different tempos you have to make sure the time base is set to "Beats". This means the item sticks on the beat and stretches according to it. Changing the tempo changes the playrate then.
If I misunderstood your problem, please describe it more accurate. The chance of getting help increases with the posting details and screen shots.
Greeting
Eli
Change loop selection while you change song bpm
Linear Mode
