If DOSBox is started in window mode, the Return key won't resopnd in Tomb Raider. Starting DOSBox in fullscreen is ok. Similarly, if I start DOSBox in fullscreen and then switch to windowed, the Return key won't respond.
This happens about 99% of the time.
If you switch to fullscreen before Tomb Raider starts (while DOS/4GW is still showing) then there is no issue.
I've just tested r4052, and this issue seems to have been fixed.