I can't reproduce your problem

$ perl -de0

Loading DB routines from perl5db.pl version 1.53
...
  DB<1> $_='1223w3433.45+34'

  DB<2> x /\d\D*/g
0  1
1  2
2  2
3  '3w'
4  3
5  4
6  3
7  3.
8  4
9  '5+'
10  3
11  4
  DB<3> p $]
5.028002
  DB<4>
[download]

I concur with the others that you most likely changed pos in a previous step.