In some cases, running something in TextMate which outputs spaces, then copying that using the "copy output" link in the output window and then pasting it in a new TextMate document, it will paste the spaces as no-break spaces [1].
The easiest way to reproduce this is to run the following Ruby code inside TextMate:
puts ' '
Then follow the steps described above. Note that if I copy the output by selecting the text and copying it manually there's no problem.
[1] http://www.fileformat.info/info/unicode/char/00a0/index.htm