We are currently using a developer that knows php very well. But his schedule is getting very busy and they do not have time for us much anymore. We spend about 10-20 hours a month on customization requests to our mantis system. We have it integrated with the database software Filemaker Pro. Experience in Filemaker integration is a plus but is not required as the custom code is mostly on the mantis side and is independent of the link.
We do not have in-house php developers but need to keep changing the product we have. It currently does much more then bug tracking, it does time tracking, time sheets, invoicing, inventory, etc... but its using the mantis foundation.
If you work for a company that would be best but individuals would also be considered.