you have to use photobucket's app to post. nothing will load from the phone itself. i have been trying for years and always end up going back to photobucket
I just click the top right box with arrow to reply to thread. Then the + box on the top right next to the send box. Select Attach From Photos. Tap on the picture you want. It will download at the bottom under Image Attachment and will read Done Uploading. Tap on that and then on Insert Inline. Picture will then be on your New Reply. Type you reply and after that tap Send.