CellProfiler development is discussed on the cellprofiler-dev mailing list. This is a fairly low-volume mailing list. To subscribe:
https://groups.google.com/a/broadinstitute.org/d/forum/cellprofiler-dev
There is a special form for submitting new issues with attachments.
Please attach sufficient information to reproduce the bug. For many bugs, it is appropriate to attach a CellProfiler pipeline and an image.