[Floyd R Turbo]

Huh...that's odd. A few things you might try:

1) Clean the edge (and the other surface you are bonding to) with denatured alcohol instead of isopropyl. Isopropyl contains other ingredients which might be leaving a bit of residue, i.e. water.

2) blow off the edge/surface with compressed air after cleaning

3) when you set up the joint (assuming you are using a right-angle jig and the pins method) the last step before filling the joint with solvent should be to blow it out with canned air, this will de-ionize the material to an extent and get rid of any dust particles, which will hold air around them via static electricity

4) when you start the solvent, squeeze some air out, tip the bottle over to needle in position a hair beyond the edge of the joint while releasing the pressure, then start squeezing such that the tip of the needle is barely at the start of the joint, let the solvent suck into the joint ahead of the path of motion you will follow, then start moving, keeping the "bead" about 1/4" to 1/2" ahead of the needle. Finish up by ending the pass to the edge of the joint before fully releasing the presure.

Some of these you probably already know, but all the same, that's what I do