Well, there may not be a problem. Do you have a humidity gage? If not I would get one ASAP since you want to control it closely versus just spraying it down. For instance, this summer, it has been so humid we mist only at dusk to about 85%, that drops to a low in the day of around 40%. Too much water can lead to mold and mildew growth in the substrate.
The only other things I can think of is: Was the glass well cleaned and rinsed before you put in the gecko? (residue is bad!) Is s/he slipping after you handle it? (some people have noticed that skin oils can reduce their stickiness for a time afterward.)
I know when we first brought our baby crested home she couldn't stay stuck to the container we moved her in, but once she was settled in her tank she's fine. Maybe she is just playing with you? As long as the glass was well cleaned and rinsed really well, I don't think you haven anything to worry about, s/he may just be playing "slide" for all we know!
-----
0.1 Albino Leo Gecko
0.1 Crested Gecko
1.0 Dear Boyfriend
Departed: Harvey and Spock