Started a new single player game and spawned in a jungle-tree filled city. For some reason, the axe doesn't work at all to chop a jungle tree log block unless you hold down crouch to disable veinmining. If you try to break it normally it will just loop from 0% to 100% and never break the block or veinmine the entire tree.

Edit: So after more testing, it seems that it's only the naturally generated trees that are bugging out. Trees that I've planted myself veinmine just fine.

This is an issue with there simply being too many trees linked together. Find some place that's less crowded with trees, or create breaks in the tree connections manually.

Unfortunately I cannot fix this, as it is inside the code of GTCE itself.