Land border crossing to Cambodia (Poipet etc) are not going smoothly since Sept 13. If you are getting a multiple entry visa should be ok, but those of you wanting fresh land border stamps (there and back) are not working from today onward.
Breaking News! Every Thai-Cambodian border check point will not stamp 15 or 30 day visa waiver stamp, effective 13th September 2015 onwards. People with valid Multiple Entry Thai Visa have no problem, it is OK to activate your second or third entry of a Tourist Visa or a valid Multiple Entry Non Immigrant Visa. Condition to leave Thailand if you have extension of stay based on Non B or Non ED visa, please check with us!
This is according to: http://www.thaivisaservice.com
Good luck!